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Edmund P. Green and Frederick T. Short 

a group of about sixty 

species of underwater marine flowering plants, grow in 

the shallow marine and estuary environments of all the 

world’s continents except Antarctica. The primary food 

of animals such as manatees, dugongs, and green sea 

turtles, and critical habitat for thousands of other ani- 

mal and plant species, seagrasses are also considered 

one of the most important shallow-marine ecosystems 

for humans, since they play an important role in fishery 

production. Though they are highly valuable ecologically 

and economically, many seagrass habitats around the 

world have been completely destroyed or are now in 

rapid decline. The World Atlas of Seagrasses is the first 

authoritative and comprehensive global synthesis of the 

distribution and status of this critical marine habitat. 

Illustrated throughout with color maps, photographs, 

tables, and more, and written by an international team 

of collaborators, this unique volume covers seagrass 

ecology, scientific studies to date, current status, 

changing distributions, threatened areas, and conserva- 

tion and management efforts for twenty-four regions of 

the world. As human populations expand and continue 

to live disproportionately in coastal areas, bringing new 

threats to seagrass habitat, a comprehensive overview 

Digitized by the Internet Archive 
in 2010 with funding from 
UNEP-WCMC, Cambridge 

World Atlas of Seagrasses 

Published in association with 
UNEP-WCMC by the University of 
California Press 

University of California Press 
Berkeley and Los Angeles, California 
University of California Press, Ltd. 
London, England 

© 2003 UNEP World Conservation Monitoring Centre 

219 Huntingdon Road 

Cambridge CB3 ODL, UK 

Tel: +44 (0) 1223 277 314 

Fax: +44 (0) 1223 277 136 



No part of this book may be reproduced by any means 
or transmitted into a machine language without the 
written permission of the publisher. 

The contents of this volume do not necessarily reflect 
the views or policies of UNEP-WCMC, contributory 
organizations, editors or publishers. The designations 
employed and the presentations do not imply the 
expression of any opinion whatsoever on the part of 
UNEP-WCMC or contributory organizations, editors or 
publishers concerning the legal status of any country, 
territory, city or area or its authority, or concerning the 
delimitation of its frontiers or boundaries or the 
designation of its name or allegiances. 

Cloth edition ISBN 

Cataloging-in-publication data is on file with the Library 
of Congress 

Citation Green EP. and Short F.T. (2003) World Atlas of 
Seagrasses. Prepared by the UNEP World Conservation 
Monitoring Centre. University of California Press, 
Berkeley, USA. 

World Atlas of Seagrasses 
Edmund P. Green & Frederick T. Short 





World Atlas of Seagrasses 

Prepared by 

UNEP World Conservation 
Monitoring Centre 

219 Huntingdon Road 
Cambridge CB3 ODL, UK 

Tel: +44 (0) 1223 277 314 

Fax: +44 (0) 1223 277 136 

Mark Collins 

Scientific editors 
Edmund P. Green 
Frederick T. Short 

Assistant scientific editor 
Michelle Taylor 

Corinna Ravilious 

Technical editor 
Catherine Short 

Yves Messer 

A Banson production 
27 Devonshire Road 
Cambridge CB1 2BH, UK 

Color separations 

Printed in China 

Jackson Estuarine Laboratory contribution number 



The UNEP World Conservation Monitoring Centre is the 
biodiversity assessment and policy implementation arm 
of the United Nations Environment Programme (UNEP), 
the world’s foremost intergovernmental environmental 
organization. UNEP-WCMC aims to help decision- 
makers recognize the value of biodiversity to people 
everywhere, and to apply this knowledge to all that they 
do. The Centre's challenge is to transform complex data 
into policy-relevant information, to build tools and 
systems for analysis and integration, and to support the 
needs of nations and the international community as they 
engage in joint programs of action. 

UNEP-WCMC provides objective, scientifically rigorous 
products and services that include ecosystem assess- 
ments, support for implementation of environmental 
agreements, regional and global biodiversity in- 
formation, research on threats and impacts, and 
development of future scenarios for the living world. 

lllustrations in Appendix 3 and at foot of pages: 

Mark Fonseca: Zostera marina 

Phillips RC, Menez EG [1988]. Seagrasses. Smithsonian 
Contributions to the Marine Sciences 34. Smithsonian 

Institution Press, Washington DC: Zostera asiatica 

QDPI Northern Fisheries Centre, Cairns: Halophila australis, 
Halophila capricorn 

Ron Phillips: All remaining illustrations 

Supporting institutions 

Supporting institutions 


Department for 

The David and Lucile 
Packard Foundation 


International Coral Reef Action Network 

Intemational Council for Science 

Scientific Committee on Oceanic Research 

The United Nations Environment Programme is the principal United Nations body in the field of the 
environment. Its role is to be the leading global environmental authority that sets the global 
environmental agenda, promotes the coherent implementation of the environmental dimension of 
sustainable development within the United Nations system and serves as an authoritative advocate for 
the global environment. 

The UK Department for Environment, Food and Rural Affairs is working for sustainable development: 
a better quality of life for everyone, now and for generations to come. This includes a better environ- 
ment at home and internationally, and sustainable use of natural resources; economic prosperity 
through sustainable farming, fishing, food, water and other industries that meet consumers’ 
requirements; thriving economies and communities in rural areas and a countryside for all to enjoy. 

The Department for International Development is the UK Government department working to 
promote sustainable development and eliminate world poverty. This publication is an output from a 
research program funded by DFID for the benefit of developing countries. The views expressed are not 
necessarily those of DFID. 

The David and Lucile Packard Foundation, started in 1964, provides international and national support 
to non-profit organizations in conservation, science and many other areas. The foundation currently 
provides funding to SeagrassNet, a global seagrass monitoring program based at the University of 
New Hampshire. http://www.packard. org/, 

The University of New Hampshire is a land-grant, sea-grant and space-grant public institution with 
10 000 undergraduate and 2 000 graduate students, and a well-established marine program. The 
Jackson Estuarine Laboratory is the primary marine research organization at UNH and has a strong 
seagrass research component., 

The World Seagrass Association is committed to the science, protection and management of the 
seagrass ecosystem worldwide. The members come from many countries and include leading 
scientists in marine and seagrass biology. The association supports training and information 
exchange and raises global awareness of seagrass science and environmental management issues. 

The Convention on Wetlands, signed in Ramsar, Iran, in 1971, is an intergovernmental treaty which 
provides the framework for local, regional and national actions for the conservation and wise use of 
wetlands and their resources. There are presently 135 Contracting Parties to the Convention, with 
1 230 wetland sites, totaling 105.9 million hectares, designated for inclusion in the Ramsar List of 
Wetlands of International Importance. 

The International Coral Reef Action Network is an innovative and dynamic global partnership of many 
of the world's leading coral reef science and conservation organizations. Established in 1999 to halt 
and reverse the decline of the health of the world's coral reefs the partnership draws on its partners’ 
investments in reef monitoring and management to create strategically linked actions at local, 
national and global scales. 

The Scientific Committee on Oceanic Research (SCOR) was the first interdisciplinary body formed by 
the International Council for Science. SCOR activities focus on promoting international cooperation in 
planning and conducting oceanographic research. 

The Estuarine Research Federation (ERF) is a private, non-profit organization. The federation was 
created in 1971 to address broad estuarine and coastal issues; it holds biannual international 
meetings and supports the scientific publication Estuaries. 




a special mention and deserve extra thanks. First and foremost amongst these are the 58 authors who have given 

freely and extensively of their time and experience in writing the 25 chapters that constitute this World Atlas. 
Without their attention to detail and efforts in sourcing data outside the mainstream scientific literature this book 
would not have been possible. The contributions of the assistant scientific editor, Michelle Taylor, the cartographer, 
Corinna Ravilious, and technical editor, Catherine Short, have been equally invaluable in the synthesis of information 
from many hundreds of disparate sources and for ensuring consistency throughout every section. The editors have a 
particular debt of gratitude to all these people. 

The origins of the World Atlas of Seagrasses go back to late 1997 when the need for a global compendium of 
information on seagrasses was first acknowledged. Hans de Jong, Eddie Hegerl, Paul Holthus, Richard Luxmore and 
the participants at the third International Seagrass Biology Workshop, 19-26 April 1998, Manila and Bolinao, 
Philippines, were particularly helpful in pulling these ideas together. Nicholas Davidson, Salif Diop, Will Rogowski, 
Ed Urban, Genevieve Verbrugge and Marjo Vierros provided great support during the fundraising, support which was 
instrumental in making the necessary resources available. We are, of course, notably grateful to our sponsors, listed 
at the beginning of the World Atlas, for investing funds in this work. Special mention is due here to the David and 
Lucile Packard Foundation and University of New Hampshire for supporting Fred Short’s time. 

A long period of data collection followed soon after work began and involved much detailed correspondence with 
very many people. Our thanks go out to everyone who answered our ‘phone calls and e-mails, but even more so to 
those who provided us with seagrass distribution data or maps, especially William Allison, Alex Arrivillaga, Susanne 
Baden, Seth Barker, David Blackburn, Simon Blyth, Christoffer Bostrom, Nikki Bramwell, Marnie Campbell, Jacoby 
Carter, Rob Coles, Helen Cottrell, Lucy Conway, Charlie Costello, Jeffrey Dahlin, Dick de Jong, Karen Eckert, Caroline 
Erftemeijer, Randolph Ferguson, Mark Finkbeiner, Terence Fong, Mark Fonseca, Sarah Gage, Martin Gullstrom, Rob 
Hughes, Herman Hummel, Hitoshi lizumi, Chung It Choi, Emma Jackson, Pauline Kamermans, Hilary Kennedy, Ryo 
Mabuchi, lan May, Pete McLain, Thomas Meyer, Mark Monaco, Kenji Morita, lvan Nagelkerken, Brian Pawlak, Karin 
Pettersson, Ron Phillips, Martin Plus, Chris Pickerell, Jean Pascal Quod, Thorsten Reusch, Ron Rozsa, Jan Steffen, 
Marieke van Katwijk, Mikael von Numers, Rob Williams, Lisa Wood, Masumi Yamamuro and members of the Wider 
Caribbean Sea Turtle Conservation Network [WIDECAST): Timothy Austin, Andy Caballero, Didiher Chacon, Juan 
Manuel Diaz and Alan Mills. Clearly a number of data sharing agreements were necessary as these data were 
identified and we thank Mary Cordiner for sorting out these institutional complexities. 

The coordinators of the Global Seagrass Workshop, Mark Spalding and Michelle Taylor, and all 23 delegates 
(page 283] are gratefully acknowledged for the time and effort they made to review, amend and correct the seagrass 
distribution data. The workshop itself would not however have been possible without considerable logistic and 
organizational support from Janet Barnes, Joy Bartholomew, Jean Finlayson, Anne Giblin, Pam Price, Ed Urban and 
Susan White, also all the staff at the Tradewinds Hotel, St Petersburg Beach, Florida. 

Jamie Adams, Mary Edwards and Sergio Martins have provided additional geographical information systems 
support at various stages during the preparation of the maps for the World Atlas and Elizabeth Allen, Janet Chow, 
Mary Cordiner and Michael Stone have spent very many long hours formatting and organizing the reference sections 
for the chapters and on-line bibliography ( 

Readers will quickly note the wonderful photographs which have been kindly donated. Credit is given next to 
individual photographs but thanks are also due here to Nancy Diersing, Florence Jean, Karine Magalhaes, Kate 
Moran and John Ogden all of whom helped us track down owners of pictures which we wanted to use. Most of the 
drawings of seagrasses in Appendix 3 and illustrated at the foot of the pages were donated by Ron Phillips, whom 
we especially thank for this contribution. Rob Coles, Mark Fonseca and Mike Fortes provided additional drawings for 
Appendix 3 and the page corners, and we thank them as well. 

When reviewing correspondence and notes spanning the last five years it is all too easy to overlook or forget 
someone. Sincere apologies to anyone whom we have neglected to mention here. Please be assured that this was 
simply an oversight brought about by the effort of completing the book and nothing else! 

T: World Atlas of Seagrasses is a product of global collaboration between many different people but a few merit 

Ed Green and Fred Short 



Centre. The World Summit on Sustainable Development adopted, in the area of biodiversity, a 

commitment to reverse the trend of losses by 2010. To achieve this we need hard facts on which to 
base decisions. The World Atlas of Seagrasses meets that need for a vital marine ecosystem whose 
importance has largely been overlooked until now. 

| t is with great pleasure that | introduce this new book from the UNEP World Conservation Monitoring 

This book would not have been possible without a remarkable collaboration between the 58 authors from 
25 countries. The World Atlas of Seagrasses has played a role in fostering international collaboration by 
gathering information from many different sources all over the world. On behalf of UNEP | would like to 
express my gratitude to all the authors who have contributed their knowledge. 

| would also like to thank the sponsors of the World Atlas of Seagrasses including the UK Department for 
Environment, Food and Rural Affairs, the UK Department for International Development, the Secretariat 
of the Ramsar Convention on Wetlands, the David and Lucile Packard Foundation, the University of New 
Hampshire, the World Seagrass Association, the Scientific Committee on Oceanic Research, the 
Estuarine Research Federation and the International Coral Reef Action Network. 

| am confident that this book will help not only UNEP but all interested parties to focus on the 

implementation of sustainable development in the marine environment worldwide. 

Klaus Toepfer 
Executive Director, United Nations Environment Programme (UNEP) 





maestros that take center stage. It is true that rain forests, coral reefs, whales, tigers and the like 

carry an important representational role as they fill our television screens and become a priority in our 
conservation programs. But we should not forget the many other ecological players that make up 
nature’s orchestra. The living world is an interactive and integrated continuum that we partition into 
ecosystems for our own scientific convenience. The less well-known ecosystems often play a distinct and 
very important part in the overall harmony that we need to maintain, but only poorly understand. One 
such ecosystem is the beds of seagrass that are found on coastlines around the world. 

Seagrass beds are unusual in that they are very widespread, occurring on shallow coastlines in all 
but the coldest waters of the world. A small group of flowering plants, just 60 among the 270 000 species 
of fish, plants and other organisms that have colonized the sea, they owe their success to this ability to 
tolerate a wide range of conditions. So why have they been selected for this global report? 

First of all, seagrass beds are an important but under-rated resource for coastal people. Physically 
they protect coastlines from the erosive impact of waves and tides, chemically they play a key role in 
nutrient cycles for fisheries and biologically they provide habitat for fish, shellfish and priority ecotourism 
icons like the dugong, manatee and green turtle. And yet, despite these important attributes, they have 
been overlooked by conservationists and coastal development planners throughout their range. 

This World Atlas of Seagrasses is literally putting seagrass beds onto the map, for the first time. It is 
a groundbreaking synthesis that provides people everywhere with the first world view of where seagrasses 
occur and what has been happening to them. It is a worrying story. Seagrass beds have been needlessly 
destroyed for short-term gain without real analysis of the values that the intact ecosystems bring to 
coastal society. There is no proper strategy for their protection. Their significance is not well appreciated 
and awareness is very low. This World Atlas will go a long way towards reversing these trends. 

As ever in the production of an analysis of this kind, our scientists at the UNEP World Conservation 
Monitoring Centre have been able to achieve their results only by standing on the shoulders of giants. We 
acknowledge and applaud the dedicated band of seagrass ecologists and taxonomists who have laid the 
groundwork for this World Atlas and prepared much of the text. | hope it will bring well-deserved 
recognition for them and for their seagrasses, and establish a baseline from which to build a more 
sustainable future for coastal peoples and the home of the gentle dugong. 

| n describing the complex relationships that exist in the living world we all too often focus on the 

Mark Collins 
Director, UNEP-WCMC 





Introduction to the World Atlas of Seagrasses 
Key to maps and mapping methods 


The distribution and status of seagrasses 

] World seagrass distribution 

2 Global seagrass biodiversity 


1 Relative size-frequency distribution of 

538 seagrass polygons in latitudinal 
swathe 20-30°S 
2 Growth of marine protected areas which 

include seagrass ecosystems, shown both 
as the number of sites [line] and the total 

area protected (shaded area] 


1 A list of seagrass species by family 

2 Major taxonomic groups found In 
seagrass ecosystems, with brief notes 

3 Threatened species regularly recorded 
from seagrass communities worldwide 

4 Estimates of seagrass coverage for 
selected areas described in this 
World Atlas 

5 Functions and values of seagrass from 

the wider ecosystem perspective 
6 Summary of the goods and services 
provided by seagrass ecosystems 

Uf Summary of marine protected areas that 

contain seagrass ecosystems, from the 

UNEP-WCMC Protected Areas Database 

1 THE SEAGRASSES OF Scandinavia and the Baltic 
1.1. Scandinavia 
1.1 Average (+1 SE) above-ground biomass 
values for eelgrass (Zostera marina] 
along the Baltic Sea coastline 

1.2 Aerial photographs of two typical exposed 

eelgrass (Zostera marina] sites at the 
Hanko Peninsula, southwest Finland 







3 Norwegian eelgrass coverage 

-4_ Map of eelgrass area distribution in 
Danish coastal waters 

.5 Maximum colonization depth of 
eelgrass patches in Danish estuaries 
and along open coasts in 1900 and 

.6 Secchi depths and maximum 
colonization depths of eelgrass patches 
in Danish estuaries and open coasts in 
1900 and 1992 

1.7. Long-term changes in the distribution 

of eelgrass (Zostera marina} in the 

southeastern Baltic Sea [Puck Lagoon, 


2 THE SEAGRASSES OF Western Europe 


2.1. Western Europe (north) 
2.2 Western Europe [south] 

2.1. The Wadden Sea 

2.2. Glénan Archipelago 

THE SEAGRASSES OF The western Mediterranean 

3.1 The western Mediterranean 

3.1 Italy 

3.2. France 

3.3 Spain 


3.1 Examples of general features of 
Mediterranean seagrass meadows 

3.2 Distribution of seagrasses throughout 
the western Mediterranean (Italy, France 
and Spain] 

THE SEAGRASSES OF The Black, Azov, Caspian 
and Aral Seas 


4.1 The Black, Azov, Caspian and Aral Seas 

THE SEAGRASSES OF The eastern Mediterranean 
and the Red Sea 


5.1. The eastern Mediterranean 

5.2 The Red Sea 


5.1 Israeli coast of the Gulf of Elat 











6 THE SEAGRASSES OF The Arabian Gulf and Arabian 9.2 Occurrence of seagrasses in coastal 
region 74 states of India 104 
Map 9.3 Associated biota of seagrass beds of 
6.1. The Arabian Gulf and Arabian region 75 India 105 
6.1. The Bahrain Conservancy 76 10 THE SEAGRASSES OF Western Australia 109 
6.2 Rapid assessment technique 77 Map 
6.3 Marine turtles and dugongs in the 10.1 Western Australia 111 
Arabian seagrass pastures 79 Case STUDY 
TABLE 10.1 Shark Bay, Western Australia: How 
6.1 Seagrass species in the Arabian region 75 seagrass shaped an ecosystem 116 
7 THE SEAGRASSES OF Kenya and Tanzania 82 10.1 Western Australian endemic seagrass 
MAP species 110 
7.1. Kenya and Tanzania 83 10.2. Summary of major human-induced 
CASE STUDIES declines of seagrass in Western 
7.1 Gazi Bay, Kenya: Links between Australia 113 
seagrasses and adjacent ecosystems 84 
7.2 Seagrass beach cast at Mombasa 11 THE SEAGRASSES OF Eastern Australia 119 
Marine Park, Kenya: A nuisance or a MAP 
vital link? 88 11.1 Eastern Australia 121 
8 THE SEAGRASSES OF Mozambique and 11.1. Mapping deepwater (15-60 m) 
southeastern Africa 93 seagrasses and epibenthos in the 
MAPS Great Barrier Reef lagoon 124 
8.1 Mozambique and southeastern Africa 94 FIGURE: Probability of the occurrence 
8.2 The Seychelles 94 of deepwater seagrasses in the Great 
8.3 Mauritius 94 Barrier Reef Lagoon 
Case STUDY FIGURE: Frequency of the probability of 
8.1. Inhaca Island and Maputo Bay area, occurrence of seagrasses within each 
southern Mozambique 96 depth stratum 
FIGURE 11.2 Westernport Bay 126 
8.1 Digging of Zostera capensis meadows FIGURE: Distribution of estuarine 
at Vila dos Pescadores, near Maputo city 99 habitats in Westernport Bay, Australia 
TABLES 11.3. Expansion of Green Island seagrass 
8.1 Area cover and location for the meadows 128 
seagrass Zostera capensis in South FIGURE: Seagrass distribution at Green 
Africa 94 Island in 1994, 1972, 1959 and 1936 
8.2 Seagrass cover and area lost in 
Mozambique 99 12 THE SEAGRASSES OF New Zealand 134 
9 THE SEAGRASSES OF India 101 12.1 New Zealand 135 
9.1 India 103 12.1 A seagrass specialist 140 
9.2 Andaman and Nicobar Islands 103 FIGURE 
CASE STUDY 12.1 An example of changes in the historical 
9.1 Kadmat Island 106 distribution of seagrasses in New 
TABLE: Characterization of a seagrass Zealand 139 
meadow at Kadmat Island, TABLES 
Lakshadweep 12.1 Area of seagrass in New Zealand 
TABLE: Benthic macrofauna in the estuaries where benthic habitats have 
seagrass bed at Kadmat Island, been mapped 135 
Lakshadweep 12.2 List of locations where seagrasses have 
FIGURE been recorded in New Zealand 136 
9.1 Abundance of seagrass species at 
various depths in the Gulf of Mannar 13 THE SEAGRASSES OF Thailand 144 
{southeast coast) 105 Map 
TABLES 13.1 Thailand 145 
9.1 Quantitative data for major seagrass CASE STUDY 

beds in Indian waters 102 13.1 The dugong - a flagship species 147 

13.1 Occurrence of seagrass species in 



14.1 Peninsular Malaysia 

14.2 Sabah 


14.1 The seagrass macroalgae community 
of Teluk Kemang 

14.2 The subtidal shoal seagrass community 
of Tanjung Adang Laut 

14.3 Coastal lagoon seagrass community at 
Pengkalan Nangka, Kelantan 


14.1. Estimate of known seagrass areas in 
Peninsular Malaysia 

15 THE SEAGRASSES OF The western Pacific islands 


15.1 Western Pacific islands (west) 

15.2 Western Pacific islands [east] 


15.1 Kosrae 
Maps: Lelu Harbour ca 1900 and 1975; 
Okat Harbour and Reef 1978 and 1988 

15.2 SeagrassNet - a western Pacific pilot 



16.1. Indonesia 


16.1 Banten Bay, West Java 

16.2 Kuta and Gerupuk Bays, Lombok 

16.3 Kotania Bay 
TABLE: Distribution of seagrass 


16.1 Average biomass of seagrasses at 
various locations throughout 

16.2 Average density of seagrasses at 
various locations throughout the 
Indonesian Archipelago 

16.3 Average shoot density of seagrass 
species in mixed and monospecific 
seagrass meadows in the Flores Sea 

16.4 Average growth rates of seagrass 
leaves using leaf-marking techniques 

16.5 Indonesian seagrass-associated flora 
and fauna: number of species 

16.6 Present coverage of seagrasses in 

The Philippines and Viet Nam 


17.1. Japan 














17.1. Akkeshi, eastern Hokkaido 

17.2 Rias coast in Iwate Prefecture, 
northeastern Honshu 


17.1 Seagrasses recorded in Japan 

17.2 Traditional uses of seagrasses in Japan 

17.3 Estimates of total areas of algal and 
seagrass beds in Japan in 1978 and 
1991, and the percent area lost 

18 THE SEAGRASSES OF The Republic of Korea 


18.1 Republic of Korea 


18.1 Recent research on seagrasses 


18.1 Physical characteristics of seagrass 
beds on the west, south and east coasts 
of the Republic of Korea 

18.2 Seagrass species distributed on the 
coasts of the Republic of Korea 

18.3 Habitat characteristics of seagrass 
species in the Republic of Korea 

18.4 Morphological characteristics of 
seagrasses distributed in the Republic 
of Korea 

18.5 The estimated areas of seagrasses 
distributed on the coasts of the Republic 
of Korea 

19 THE SEAGRASSES OF The Pacific coast of North 



19.1. The Pacific coast of North America 


19.1. The link between seagrass and 
migrating black brant along the Pacific 

19.2 The link between the seagrass Zostera 
marina (ts ‘ats ‘ayem] and the 
Kwakwaka wakw Nation, Vancouver 
Island, Canada 

19.3. The link between seagrasses and 
humans in Picnic Cove, Shaw Island, 
Washington, United States 


19.1 Zostera marina and Zostera japonica 
basal area cover in the Northeast Pacific 

20 THE SEAGRASSES OF The western North Atlantic 


20.1 The western North Atlantic 


20.1 Portsmouth Harbor, New Hampshire 
and Maine 
FiGuRE: Eelgrass distribution by depth 

in Portsmouth Harbor, Great Bay Estuary, 

on the border of New Hampshire and 
Maine, United States 

























20.2 Ninigret Pond, Rhode Island 211 
FIGURE: Eelgrass distribution in Ninigret 
Pond, Rhode Island (United States] 
plotted by depth for 1974 and 1992 
FIGURE: Change in eelgrass area in 
Ninigret Pond, Rhode Island (United 
States] plotted against increasing number 
of houses in the watershed 

20.3 Maquoit Bay, Maine 213 


20.1 The area of eelgrass, Zostera marina, 
in the western North Atlantic 212 



THE SEAGRASSES OF The mid-Atlantic coast of 
the United States 216 
21.1. The mid-Atlantic coast of the United 
States 217 
21.1 Seagrasses in Chincoteague Bay: a 
delicate balance between disease, 
nutrient loading and fishing gear impacts 220 
FIGURE: Recovery and recent decline of 
seagrass (Zostera marina and Ruppia 
maritima} distribution in Chincoteague Bay 
FIGURE: Aerial photograph taken in 1998 of 
a portion of Chincoteague Bay, Virginia, 
seagrass bed showing damage to the bed 
from a modified oyster dredge 
21.1 Seagrass distribution (mainly Zostera 
marina and Ruppia maritima) in 
Chesapeake Bay 218 
21.2 Changes in seagrass (Zostera marina 
and Halodule wrightii) distribution in 
the Cape Lookout area [southern Core 
Sound, North Carolina) between 1985 
and 1988 218 

22 THE SEAGRASSES OF The Gulf of Mexico 224 
22.1 The Gulf of Mexico 225 
22.1 Tampa Bay 226 
22.2 Laguna Madre 228 
FIGURE: Seagrass cover in the Laguna 
Madre of Texas 
22.3 Laguna de Términos 231 

23 THE SEAGRASSES OF The Caribbean 234 
23.1 The Caribbean 235 


23.1 Florida's east coast 236 
23.2 Parque Natural Tayrona, Bahia de 

Chengue, Colombia 239 
23.3 Puerto Morelos Reef National Park 240 

24 THE SEAGRASSES OF South America: Brazil, 

Argentina and Chile 243 
24.1 South America 245 
24.1 |Itamaraca Island, northeast Brazil 244 
24.2 Abrolhos Bank, Bahia State, northeast 

Brazil 247 
24.3 Ruppia maritima in the Patos Lagoon 

system 248 

24.1 Cumulative number of companion 
species to the Brazilian seagrasses 

reported since 1960 245 
1 Seagrass species, by country or 
territory 251 

2 Marine protected areas known to 
include seagrass beds, by country or 

territory 256 

3 Species range maps 262 
The Global Seagrass Workshop 287 
INDEX 288 


Europe Plate |, facing p 38 
Africa, West and South Asia Plate III, facing p 102 
Australasia Plate V, facing p 118 
The Pacific Plate VII, facing p 166 
Asia Plate IX, facing p 182 
North America Plate XI, facing p 214 
The Caribbean Plate XIII, facing p 230 
South America Plate XIV, facing p 231 


The beauty of seagrasses Plate Il, facing p 39 
Impacts to seagrass ecosystems Plate IV, facing p 103 
Seagrass ecosystems Plate VI, facing p 119 
Seagrasses and people Plate VIII, facing p 167 
The sex life of seagrasses Plate X, facing p 183 
Diversity of seagrass habitats Plate XII, facing p 215 

Introduction to 



providing important ecological and economic 

components of coastal ecosystems worldwide. 
Although there are extensive seagrass beds on all the 
world’s continents except Antarctica, seagrasses have 
declined or been totally destroyed in many locations. As 
the world’s human population expands and continues 
to live disproportionately in coastal areas, a comp- 
rehensive overview of coastal resources and critical 
habitats is more important than ever. The World Atlas 
of Seagrasses documents the current global distri- 
bution and status of seagrass habitat. 

Seagrasses are a functional group of about 
60 species of underwater marine flowering plants. 
Thousands more associated marine plant and animal 
Species utilize seagrass habitat. Seagrasses range 
from the strap-like blades of eelgrass (Zostera 
caulescens) in the Sea of Japan, at more than 4 m long, 
to the tiny, 2-3 cm, rounded leaves of sea vine [e.g. 
Halophila decipiens) in the deep tropical waters of 
Brazil. Vast underwater meadows of seagrass skirt the 
coasts of Australia, Alaska, southern Europe, India, 
east Africa, the islands of the Caribbean and other 
places around the globe. They provide habitat for fish 
and shellfish and nursery areas to the larger ocean, 
and performing important physical functions of filtering 
coastal waters, dissipating wave energy and anchoring 
sediments. Seagrasses often occur in proximity to, and 
are ecologically linked with, coral reefs, mangroves, 
salt marshes, bivalve reefs and other marine habitats. 
Seagrasses are the primary food of manatees, dugongs 
and green sea turtles, all threatened and charismatic 
species of great public interest. 

Seagrasses are subject to many threats, both 
anthropogenic and natural. Runoff of nutrients and 
sediments from human activities on land has major 
impacts in the coastal regions where seagrasses thrive; 
these indirect human impacts, while difficult to 
measure, are probably the greatest threat to seagrasses 

Greve are valuable and overlooked habitats, 

worldwide. Both nutrient and sediment loading affect 
water clarity; seagrasses’ relatively high light require- 
ments make them vulnerable to decreases in light 
penetration of coastal waters. Direct harm to seagrass 
beds occurs from boating, land reclamation and other 
construction in the coastal zone, dredge-and-fill 
activities and destructive fisheries practices. Human- 
induced global climate change may well impact 
seagrass distribution as sea level rises and severe 
storms occur more frequently. The World Atlas of 
Seagrasses makes it clear that seagrasses receive little 
protection despite the myriad threats to this habitat. 
Most of our understanding of seagrass ecosystems 
is based on site-specific studies, usually in developed 
nations. Very little is known about the importance of 
seagrasses in maintaining regional or global 
biodiversity, productivity and resources, partly because 
seagrasses are under-appreciated and their distribution 
is so poorly documented. As a result, seagrasses are 
rarely incorporated specifically into coastal management 
plans and are vulnerable to degradation. Seagrass 
ecosystems in the Caribbean, Indian Ocean, Southeast 
Asia and Pacific are especially poorly researched, yet it is 
in these regions that the direct economic and cultural 
dependence of coastal communities upon marine 
resources, including seagrasses, tends to be highest. 
The purpose of the World Atlas of Seagrasses is to 
present a global synthesis of the distribution and status 
of seagrasses. Such syntheses are available for other 
coastal ecosystems and have been instrumental in 
creating awareness, driving clearer conservation and 
management efforts and focusing priorities at the 
international level. For example, over the last ten years, 
opinion on the status of coral reefs has changed from a 
predominant view that the majority of coral reefs were 
unaffected by human activities, to the present view in 
which the global decline of coral reefs, and the increas- 
ing threats to them, are widely acknowledged. A similar 
understanding of seagrass ecosystems is needed in 

Photo: M. Kochzius 


A patch reef in the Philippines surrounded by a luxuriant mixed 
bed of Thalassia hemprichii and Syringodium isoetifolium. 

order to achieve the visibility and recognition necessary 
to protect this valuable global resource. Public percep- 
tion translates into political interest. Perceptions of 
seagrass ecosystems must achieve comparable status 
with those of coral reef and mangrove ecosystems, 
through the creation of global maps, global estimates of 
loss, knowledge of human impacts to the ecosystem, 
regular monitoring of ecosystem status and a global plan 
of action to reverse seagrass ecosystem decline. It is our 
hope that the World Atlas of Seagrasses will contribute 
to the more widespread recognition, understanding, and 
protection of seagrass ecosystems worldwide. 


The World Atlas of Seagrasses is presented in two 
sections. The first section comprises a Global Overview 
of the state of our knowledge of seagrasses. It presents 
detailed ecosystem distribution and species diversity 
maps and the most accurate possible estimate of 
global seagrass area. Appendices supply seagrass 
species lists for almost 180 countries and territories, a 
list of marine protected areas known to include 
seagrasses and a collection of species range maps. The 
Global Overview was based on a compilation of 
seagrass literature and a workshop held in Florida with 
seagrass scientists from around the world contributing 
their regional knowledge and expertise. The Global 
Seagrass Workshop, sponsored by UNEP-WCMC, with 
considerable assistance from the World Seagrass 
Association, was held in St Petersburg, Florida in 
November 2001 specifically to begin assembling 
information on global seagrass distribution for the 
World Atlas (see page 287}. Twenty-three delegates 
from 15 countries participated, and all are represented 
here as chapter authors. The workshop was a forum for 
discussion on the organization of an atlas, regional 

seagrass distribution, and seagrass functions and 
threats at a global level. Later, additional chapter 
authors were asked to contribute to represent regions 
of the world not yet well covered; also, chapter authors 
invited co-authors to join their effort. The geographical 
coverage of the World Atlas reflects this process. 

The second section of the World Atlas of 
Seagrasses consists of 24 regional and national 
chapters. In each chapter, the authors have synthesized 
knowledge of seagrasses, the plants’ biogeography, 
ecology and associated species, historical perspectives 
and threats to the ecosystem as well as management 
policies pertaining to seagrasses. Wherever possible, 
the authors have estimated the area of seagrass in 
their region and summarized its status. Case studies 
throughout the chapters highlight particularly interest- 
ing seagrass habitats and areas where human or 
natural impacts to seagrasses are of concern. 

Dugong feeding on Halophila ovalis, Vanuatu, western Pacific 

Of course, any comprehensive atlas builds on 
the work of many scientists beyond the chapter 
authors. Seagrass science owes much to den Hartog’s 
Seagrasses of the World and the many subsequent 
publications and books that are referenced throughout 
the World Atlas. All of the references used to compile 
the World Seagrass Distribution Map (reproduced on 
page 21], as well as the individual chapter references, 
appear in an online bibliography at http://www. 

Photo: L. Murray 

Photo: S.0. Bandeira 

Additionally, the sources of information that contribute 
to the World Seagrass Distribution Map may be queried 
online through a GIS database at http://www-stort. Inevitably, in 
a complex collaboration of this type, some sources of 
data are overlooked. Indeed, we have become aware of 
additional sources of information on the distribution of 
seagrasses since our printing deadline. Readers with 
information on seagrass distribution that they would 
like to add to the database may contact us directly. 

The seagrass distributions mapped in this World 
Atlas were derived from scientific journals, books, other 
publications and reports, reliable websites and personal 
communications. Where these sources provided maps of 
actual seagrass beds, that mapped extent of seagrass 
(polygon) was entered directly onto the World Seagrass 
Distribution Map. More frequently, publications and 
other sources simply mention the occurrence of 

=e 52 = 
Women harvesting shellfish, Pinna muricata, from an intertidal 
seagrass flat at low tide, Matibane, Mozambique. 

seagrass at a particular location (e.g. a bay, beach, town 
or known latitude/longitude). In these cases, the 
seagrass occurrence is shown on the distribution map as 
a dot, designating the mentioned location. The World 
Seagrass Distribution Map at the beginning of the World 
Atlas gives the compilation of all the available 
information on seagrass distribution, as both actual beds 
and as locations indicated by dots, of all seagrass 
species combined. Species range maps (in Appendix 3) 
depict the area where a certain seagrass species may be 


Eutrophication reduces water clarity and stimulates growth of 
epiphytic algae, as on this Zostera marina in southern Norway. 

expected to occur, based on individual species reports 
collected for the World Seagrass Distribution Map. Using 
an overlay of all the species range maps, a global map of 
seagrass species diversity was created (reproduced on 
page 22). Additionally, regional maps show the same 
information as the World Seagrass Distribution Map, but 
at a finer scale and with the locations of the case studies 
in the region. Finally, each of the chapters has its own 
map, showing seagrass distribution and important 
locations discussed in the chapter. 


The synthesis represented by the World Atlas of 
Seagrasses confirms that seagrasses are one of the 
most widespread marine ecosystems, quite possibly 
the most widespread shallow marine ecosystem, in the 
world. They cover an area that can only be crudely 
estimated at present; the area we are able to document 
in the World Atlas is certainly a gross underestimate. 
The threats to seagrasses worldwide are similar and 
widespread. Seagrasses everywhere are vulnerable to 
eutrophication from nutrient over-enrichment of the 
environment and to turbid conditions caused by upland 
clearing and disturbance, both leading to reduced light 
availability. Seagrasses are also subject to total 
destruction through coastal construction and other 
direct human impacts. Direct use of seagrass plants by 
humans is limited, but seagrass beds support impor- 
tant coastal fisheries worldwide, and because they 
occur in easily accessible, shallow, sheltered areas 
these are often subsistence fisheries. Seagrasses are 
an important coastal ecosystem in need of more study, 
awareness and protection. 

Ed Green 
Fred Short 

Photo: C. Bostrom 


Essential information 


Seagrass (location only, extent unknown) 

Seagrass area 

Number of species (map page 22) 






The seagrass features mapped throughout this World Atlas were derived 
from very many different sources. Selection criteria were used when 
reviewing thousands of records from hundreds of sources to determine 
which features would be mapped. 

The approach adopted was one that minimized subjectivity. For 
example a statement such as " Gerupuk Bay, southern Lombok, 
Halodule uninervis densities ranged from...” (page 173] would result in a 
point at that location. At the scale of a global atlas a point in Gerupuk Bay 
is sufficiently accurate. Statements such as “extensive terracing of these 
expanses of the intertidal zone [of the Kimberley Coast, Western 
Australia] often results in seagrass, particularly Enhalus acoroides, high 
in the intertidal just below the mangroves” (page 110] have not been 
recorded on the maps because no exact locations or extent of seagrass 
were available. At the scale of a global atlas an assumption that seagrass 
occurs along large sections of the Kimberley coast would have been too 
inaccurate without independent reference. Some islands or coastal areas 
have comprehensive coverage on the maps. These are derived from 
studies where an entire area has been mapped in great detail, often using 
aerial photography or satellite remote sensing. Corsica is one example” 
and the data were available for inclusion in the World Atlas maps. The 
decision to construct the maps only on referenced sources [e.g. Corsica) 


m meter mg milligram 
km kilometer g gram 

ha hectare kg kilogram 
cm/s centimeters per second kcal calorie 

0-200 m 
200-2000 m 
a >2000 m 

Species range maps (Appendix 3) 




and not extrapolation from rather inexact statements le.g. the Kimberley 
Coast] does create some apparent discrepancies but in all cases these 
are due to this decision. As such the collected total of seagrass features 
mapped in the World Atlas should be regarded as a minimal 
representation of actual coverage. 

Two further rules were applied to the making of the seagrass 
maps. Firstly, in some cases only crude maps were available, often 
covering very large areas with swathes simply indicative of the presence 
of seagrass [e.g. the global National Geographic 2000 Coral World map). 
They were cut to match shallow bathymetry data to avoid 
misrepresenting the depths at which seagrasses are found. Secondly, 
when no specific location was available beyond the name of a very small 
island a point was placed in the center of that island. Yap, Micronesia, is 
one example. Seagrass is recorded as occurring all around Yap with no 
more precise locators so this is recorded as a point centered on the 
island. Yap is small enough so that, at the scale at which these maps are 
most useful, a visible point covers the island entirely. 

1 Pasqualini V, Pergent-Martini C, Pergent G [1999]. Environmental 
impact identification along the Corsican coast (Mediterranean sea] 
using image processing. Aquatic Botany 65: 311-320. 

psu practical salinity units {almost 
equal to parts per thousand] 

UV ultraviolet 

°C degrees Centigrade 

Bold type is used to indicate the corresponding author and contact details at the end of each chapter. 

Global overview 

The distribution and status of seagrasses 



which grow submerged in shallow marine and 

estuarine environments worldwide. In many 
places they cover extensive areas, often referred to as 
seagrass beds or seagrass meadows. Although there 
are relatively few species of seagrass, the complex 
physical structure and high productivity of these eco- 
systems enable them to support a considerable bio- 
mass and diversity of associated species. Seagrasses 
themselves are a critically important food source for 
dugong, manatee, sea turtles and waterfowl. Many 
other species of fish and invertebrates, including sea 
horses, shrimps and scallops, utilize seagrass for part 
of their life cycles, often for breeding or as juveniles. 
Seagrasses are considered to be one of the most 
important shallow marine ecosystems to humans, 
playing a significant role in fisheries production as well 
as binding sediments and providing some protection 
from coastal erosion. 

The overview summarizes the distribution, impor- 
tance and status of seagrasses worldwide. Firstly we 
consider the definition of seagrasses, both as species 
and as habitats, and look at their geographic distribution 
patterns. Much of this work is the presentation of 
entirely new datasets that have been developed for this 
atlas, including a detailed distribution database and digi- 
tal maps compiled from numerous sources, often gener- 
ously contributed. Next we consider the importance of 
seagrasses to humans. Finally we look at human 
impacts on these ecosystems, including both threats and 
management measures for the protection of seagrass 
beds. Much of this chapter has benefited from the spec- 
ialist input of seagrass experts worldwide, and especially 
those who are also contributors to this World Atlas. 

Gites are a mixed group of flowering plants 

Seagrasses are flowering plants which grow fully 
submerged and rooted in estuarine and marine 

M. Spalding 
M. Taylor 
C. Ravilious 
F. Short 

E. Green 

environments. They are not true grasses. Although they 

are all monocotyledons, they do not have a single 

evolutionary origin, but are a polyphyletic group, 
defined by the particular ecological niche they inhabit. 

Five particular adaptations to enable survival in this 

niche have been identified": 

) an ability to grow whilst completely submerged, 
which presents problems, notably of lowered gas 
concentrations and rates of diffusion; 

fo) an adaptation to survive in high, and often varying, 

) an anchoring system to withstand water 

a submarine pollination mechanism; 
an ability to compete with other species in the 
marine environment. 

The adaptations have led to a number of 
morphological characteristics which are widespread 
amongst seagrasses, notably: flattened leaves [with the 
exception of Syringodium and some Phyllospadix spp.); 
elongated or strap-like leaves [with the exception of 
species in the genus Halophila\); and an extensive 
system of roots and rhizomes". 

Considerable arguments remain over the 
nomenclature and taxonomic relations of the sea- 
grasses, and it is likely that there will be considerable 
changes to the accepted classification in coming 
years“ and hence to the number of species con- 
sidered to be seagrasses. In the present work we have 
adopted a conservative approach, and consider 59 
species, based on species lists used in Hemminga and 
Duarte”! and in Short and Coles", with further advice 
from the authors of this World Atlas. These species 
are listed in Table 1. It is important to bear in mind, 
however, that “the actual number of seagrass species 
is a matter of debate, depending in part on their 
proximity to the marine environment and on the level 



of discrimination in 

Many species of the genus Ruppia are accepted 
as seagrasses, commonly occurring in the marine 
environment and often intermingled with other 
seagrass species”. Species in the genera Potamogeton 

physical taxonomy and 

Overview Table 1 

A list of seagrass species by family 
Genus Species Author 
Halophila johnsonii’ 
Halophila minor’ 
Halophila ovalis 
Halophila ovata’ 
Halophila spinulosa 
Halophila stipulacea 
Halophila tricostata 
Thalassia hemprichii 

(L.f.) Royle 

Doty & Stone 





Doty & Stone 

(Zollinger) den Hartog 
(R. Brown] Hooker f. 

(R. Brown) Ascherson 
(Forsskal) Ascherson 
(Ehrenberg) Ascherson 
Banks ex Konig 




{Labill.) Sonder et Ascherson 
(Black] den Hartog 

(Ucria] Ascherson 
Ehrenberg & Hemprich ex 

serrulata (R. Brown] Ascherson 
beaudette* (den Hartog) den Hartog 
bermudensis* den Hartog 

emarginata* den Hartog 

pinifolia* (Miki) den Hartog 
uninervis (Forsskal} Ascherson 
wrightii Ascherson 

Syringodium filiforme Kutzing 

Syringodium isoetifolium  {Ascherson) Dandy 
Thalassodendron _ ciliatum (Forsskal) den 


den Hartog 



Thalassodendron — pachyrhizum 

and Lepilaena are occasionally important members of 
seagrass ecosystems, but are often regarded as 
seagrass associates or facultative members of the 
seagrass community. We have included Ruppia spp. 
when they occur in marine and estuarine environ- 
ments, but these species are less well covered in the 

Genus Species Author 

Posidonia angustifolia Cambridge & Kuo 
Posidonia Hooker f. 
Posidonia Cambridge & Kuo 
[including the conspecific Posidonia robertsoniae™" 
Posidonia denhartogii* Kuo & Cambridge 
Posidonia kirkmani* Kuo & Cambridge 
(L.] Delile 

den Hartog 

Cambridge & Kuo 





asiatica Miki 

caespitosa = Miki 

capensis Setchell 

Zostera capricorni — Ascherson 

including the conspecific Zostera mucronata, Zostera muelleri and 
Zostera novazelandica™”) 

caulescens Miki 

Japonica Aschers. & Graebner 

Zostera marina Linnaeus 

Zostera noltii Hornemann 

Zostera tasmanica _ (Martens ex Aschers.] den Hartog 
(formerly Heterozostera) 
Phyllospadix iwatensis 
Phyllospadix serrulatus 
Phyllospadix torreyi 



Ruprecht ex Aschers. 
S. Watson 


Ruppia cirrhosa (Petagna] Grande 
(formerly spiralis) 

Ruppia maritima Linnaeus 

Ruppia megacarpa Mason 

Ruppia tuberosa Davis & Tomlinson 


* Species designations that are a matter of debate and currently 
under genetic and morphometric investigation. 

t Species proposed as conspecific with Halophila ovalis®’. 

literature than many other species and have not been 
universally accepted as seagrasses 

Typically, seagrasses grow in areas dominated by 
soft substrates such as sand or mud, but some species 
can be found growing on more rocky substrates [e.g 
Phyllospadix]. Seagrasses require high levels of light, 
more than other marine plants, because of their 
complex below-ground structures which include 
considerable amounts of non-photosynthetic tissues. 
Thus, although they have been recorded to 70 m in clear 
waters", they are more generally restricted to shallow 
waters due to the rapid attenuation of light with depth. 

Seagrasses can form extensive monospecific 
stands or areas of mixed species. Such areas are 
known as seagrass beds or meadows, and make up a 
unique marine ecosystem or biotope. Seagrasses can 
also grow in isolated patches, or as part of a habitat 
mosaic with other habitats such as corals, mangroves, 
bivalve reefs, rocky benthos or bare sediments 
Generally it is the larger seagrass beds and meadows 
which have been the subject of intensive study and 
mapping worldwide. Although typically permanent over 
periods of decades, seagrass systems can be highly 
dynamic, moving into new areas and disappearing from 
others over relatively short timeframes. 


In order to develop a clearer picture of the distribution of 
seagrasses worldwide, a new dataset was developed at 
UNEP-WCMC, based on literature review and outreach 
to expert knowledge. An output from this dataset is 
presented here in the World Seagrass Distribution Map 
(Map 1, which appears on page 21). 

Initial efforts focused on the acquisition of point- 
source information which was compiled into a 
spreadsheet with details on species as well as 
information on location in both descriptive terms and, 
wherever possible, geographic coordinates. This work 
continued throughout a second data-gathering phase, 
during which maps on the distribution of seagrasses 
were developed on a geographical information system 
(GIS). The two datasets remained closely linked: the 
point locations from the first phase were linked to the 
GIS, and the GIS layer also allowed for the 
incorporation of boundary information delimiting 
particular seagrass areas [polygons]. A third phase 
involved the presentation of the initial maps prepared 
by UNEP-WCMC to the Global Seagrass Workshop in 
Florida, 2001, where they were thoroughly checked by 
regional and national seagrass experts. As a result, 
new data points were added, new datasets and 
references were provided, and incorrectly located or 
Spurious data points were removed. 

At the conclusion of this effort, over 520 major 

The distribution and status of seagrasses 

Quadrat sampling in an intertidal Zostera marina bed, Maine, USA 

sources had been used in developing seagrass 
distribution data [see the online bibliography at 
references}. These sources provide information on 
seagrasses in more than 120 countries and territories 
worldwide, and the majority include information on 
specific species. All data sources were documented 
and can be queried online through the GIS (go to 

Despite the broad range of sources, the 
geographic information can be seen largely to fall into 
three categories, as discussed below. 

Direct habitat maps 

Direct habitat maps are high-resolution maps, typically 
prepared from remotely sensed data but in some cases 
mapped entirely from field observations; they 
represent the polygons showing the true spatial extent 
of seagrass distribution. They provide the most 
accurate data available for habitat distribution, but are 
available for only a very limited area worldwide. In 
some cases they do not provide species-specific 
distribution information. Sources included some 
broader maps showing seagrasses over several 
kilometers or tens of kilometers of coastline, but also 
many maps prepared and presented for individual study 
sites in expert publications. 

Expert interpolations 

In some cases, maps have been based on the 
interpolation of ground-based knowledge and 
observation - seagrasses may be known from a series 



of point locations, and with an accurate benthic chart it 
is possible to interpolate between these points to 
generate an outline of assumed seagrass area. Clearly 
the accuracy of such maps is highly variable, but can be 
relatively reliable with sufficient background infor- 
mation and cautious interpretation. These maps were 
utilized with caution and included in the GIS only if 
better data were unavailable and the source was 
considered to be reliable. 

Point-based samples 

For wide areas of the globe, maps of any sort were 
unavailable; however, it was possible to gather accurate 
point locations of seagrass beds from a large number of 
site-based seagrass publications, herbarium records 
and national species inventories. Clearly, as points, 
these give no indication of actual seagrass area, but they 
are very useful in a broader mapping context where no 
further information is available. 

Developing the distribution map 

The source maps used for producing the World 
Seagrass Distribution Map were created using many 
mapping techniques, and with various goals. There are 
also differences in resolution, which will clearly influ- 
ence the area of seagrass portrayed on a map. With 
remote sensing, accuracy is limited by the resolution 
and bandwidths utilized by the sensor, the degree of 
ground-truthing and sensitivity of the interpretation, as 
well as by the depth of the water column, the clarity of 
the water and other attributes of the benthos. Some 
remotely sensed images will pick up only shallow 
(<10 m) seagrass beds with a high shoot density, while 
large pixel size will fail to capture small or highly 
patchy seagrass areas. Error also plays a part, and 
some mapping systems may incorporate non-seagrass 
species, notably macroalgae. Although typically more 
accurate, direct sampling can have many similar 
problems, particularly associated with water depth 
and clarity. 

Combining data from multiple sources, as 
undertaken here, exacerbates these problems, as 
there are always differences in both quality and 
definition between studies. Seagrass shoot density 
varies considerably and, while some studies will 
consider only seagrass ecosystems where seagrass 
shoots are continuous at high densities [such a 
definition may in fact be forced by the mapping 
techniques], others may include all areas of even very 
sparse seagrass growth. Differences in scale between 
studies introduce further variance: lower resolution 
maps may tend to ignore minor breaks in seagrass 
beds, while finer resolution maps will pick up even 
small breaks which, it could be argued, are still a part 
of the seagrass habitat. Further problems may be 

associated with time. Seagrass systems are highly 
variable through time, with some showing seasonal 
variations and others showing dramatic interannual 
variation. Finally, it is important on a composite map, 
such as that presented here, to be aware that gaps 
where there are no data cannot be distinguished from 
gaps where seagrasses do not occur. 

The results of this data gathering have been used 
to show the distribution of individual species, and to 
show the overall distribution of seagrass habitat. The 
World Seagrass Distribution Map includes all the 
species-specific information as well as additional 
points and areas where species were not specified. 

Interpolation of the species distributions was 
used to generate species range maps (see Appendix 3). 
The known occurrences of each species were used to 
set the limits to a generalized outline of the range of 
that species. Like the raw datasets, preliminary range 
maps were reviewed at the Global Seagrass Workshop 
in Florida. It should be noted that they do not indicate 
definite occurrence of a seagrass species, but rather 
show where a species might be expected to occur 
should environmental conditions be suitable. Such 
maps are useful in biogeographic studies and 
comparisons between species, and also for predicting 
possible species occurrence in areas which have not 
been previously investigated. 

The data that constitute the World Seagrass 
Distribution Map were also used to make a preliminary 
calculation of seagrass area at global and regional 
levels. Such work has been done in more detail for 
other nearshore marine habitats'””'; however the 
weaknesses and gaps in the seagrass dataset mean 
that initial area calculations, presented below, are only 
broadly indicative. 


From the world seagrass distribution datasets 
described above, we assembled species records for 
more than 120 countries and territories. The datasets 
include some records for countries where point 
locations were unavailable [i.e. only species lists were 
available), and hence these are not shown on the maps. 
All the datasets were used to generate species lists by 
country, presented in Appendix 1. The species lists show 
that the countries with greatest seagrass diversity are 
countries which extend into both tropical and temperate 
climates, including Australia (29 species), the United 
States (23 species including all overseas territories) and 
Japan (16 species]. The greatest seagrass species 
diversity in single-climate countries occurs in the 
tropics. Tropical countries with the highest seagrass 
species diversity include India and the Philippines (both 
with 14 species) and Papua New Guinea (12 species). 
The Philippines and Papua New Guinea, together with 

Indonesia (12 species], are considered to be the center 
of global seagrass biodiversity. 

The geographic data from the same seagrass 
distribution datasets were used to generate the 
species range maps presented in Appendix 3. (Range 
maps were not prepared for Ruppia species as the 
existing data were deemed insufficient.] The species 
range maps update earlier work by den Hartog” and 
by Phillips and Menez". They show areas where the 
species may be expected to occur, but they may leave 
out some areas where seagrass information is not 

By amalgamating the species range maps, a 
global map of seagrass biodiversity was created (Map 2, 
page 22). The biodiversity map indicates the number of 
seagrass species in various parts of the globe; a 
previous effort is provided in Hemminga and Duarte™|. 
Map 2 is modeled on similar maps compiled for corals!” 

and for mangroves'"’. 

Biogeographic patterns 
Map 2 shows the three clear centers of high diversity, 
all of which occur in the eastern hemisphere. The first 
and largest of these lies over insular Southeast Asia. 
The other two centers are adjacent to this region but 
remain distinctive, being Japan/Republic of Korea 
and southwestern Australia. Other areas of 
significant diversity include southern India and 
eastern Africa. Looking at diversity patterns in more 
detail, and also at the individual species ranges that 
underpin them, it is possible to distinguish general 
regions of seagrass occurrence, each with distinctive 
floral characteristics” '”. The following list of 
seagrass regions is largely based on Short et al.'”. 

1 Tropical Indo-Pacific (IX in Short et al.'”)). 
Mirroring the biodiversity found in coral reefs and 
mangrove forests, this is a region dominated by 
tropical seagrass species, with a great focus of 
diversity in insular Southeast Asia and northern 
Australia, continued high diversity across the 
Indian Ocean and up the Red Sea, but relatively 
rapid attenuation of biodiversity across the Pacific 
islands. Key genera include Cymodocea, Enhalus, 
Halodule, Halophila, Syringodium, Thalassia and 

2. Southern Australia (X). A highly diverse region, 
dominated by temperate species. The particular 
center of diversity occurs in southwestern 
Australia (with species in the genera of 
Amphibolis, Halophila, Posidonia and Zostera). 

3 Northwestern Pacific [I]. The third-highest 
diversity region which, although connected to 
insular Southeast Asia, is dominated by 
temperate species (notably species of Zostera 
and Phyllospadix). The genus Phyllospadix is 

The distribution and status of seagrasses 

Halophila capricorni female flower, Lizard Island, Queensland, 

unique to the North Pacific, occurring in both the 
east and the west. 

4 Northeastern Pacific (I): A lower-diversity temp- 
erate area, dominated by Zostera and Phyllospadix 
species. This region is closely linked to the more 
diverse western North Pacific but also includes 
three endemic species, Phyllospadix scouleri, 
Phyllospadix serrulatus and Phyllospadix torreyi. 

5 North Atlantic [Ill]. A low-diversity temperate 
area, dominated by Zostera and Ruppia species, 
with Halodule reaching its northern limit at 35°N 
in North Carolina, USA. Europe is distinguished by 
having a second species of the Zostera genera, 
Zostera noltii. Zostera marina is the main species 
of the region. 

6 Wider Caribbean (IV). A tropical area with 
moderate seagrass diversity, including species of 
Halodule, Halophila, Syringodium and Thalassia. 
Although the tropical communities of Brazil are 
geographically isolated they are not sufficiently 
distinct to merit consideration as a separate flora 
(limited to species of Halodule, Halophila and 

7 Mediterranean [VI]. An area of relatively diverse 
temperate and tropical seagrass flora, which 
includes seagrass communities just outside the 
Mediterranean in northwest Africa as well as 
communities in the Black Sea Basin and the 
Caspian and Aral Seas. Species of Cymodocea, 
Posidonia and Zostera are common; Ruppia also 
plays an important role in the region, particularly 
in the Black, Caspian and Aral Seas. 

Photo: W. Lee Long, DPI 



8 South Africa [VIII]. The region has both temperate 
and tropical species from the genera Halodule, 
Halophila, Ruppia, Syringodium, Thalassodendron 
and Zostera. 

In addition to these floristically distinct regions 
there are three other geographically distinct seagrass 
areas which are of biogeographic interest, but which 
are poorly known and lack a distinctive floral 
characteristic, being largely depauperate. 

9 Chile [II]. One species, Zostera tasmanica 
(formerly Heterozostera), has been found along 
this coast. 

10 Southwest Atlantic [V]. Along the coast of 
Argentina and southern Chile there are extensive 
communities of Ruppia. 

11. West Africa [VII]. Only one species, Halodule 
wrightii, has been recorded; the distribution is 
poorly known. 

Considerable further work is required in order to 
understand fully the distribution patterns of sea- 
grasses; to determine the patterns of evolution and 
migration of species; and to uncover the inter- 
connections between these regions. Some of the 
patterns observed in the tropical floras mirror the 
patterns observed in corals and mangroves. The South- 
east Asian center of diversity is a particular feature of 
several marine biodiversity maps produced to date, 
including mangroves’ and several major groups of 
coral reef taxa’. It is important to distinguish this 
Southeast Asian region from the separate centers of 
diversity seen in southwestern Australia and Japan, as 
these two areas have larger ranges of climate from 
temperate to tropical (Map 2). 

Theories for the development of the Southeast 
Asian center of diversity have been advanced for a 
number of species groups. It has been variously 
suggested that this region may have been a center for 
species accumulation linked to favorable ocean 
currents (“the vortex model of coral reef bio- 
geography"; a location where high diversity was 
maintained thanks to benign climatic conditions during 
recent ice ages'”'; or a center for species evolution with 
the combination of benign conditions and changing sea 
levels ("eustatic diversity pump model"). 

The high diversity of temperate species in Japan 
and southwestern Australia is also of considerable 
evolutionary interest, but its cause remains a matter of 
speculation. There is evidence that the southwestern 
Australian flora may contain important relict 
elements'” but more recent events associated with the 
dramatic changes during and following the last ice age 
must also be considered. 

It is important to consider the evolutionary origin 

of seagrasses. The relatively low number of seagrass 
species could lead to the inference of a recent 
evolutionary history; however den Hartog” reports 
evidence for the existence of marine angiosperms as 
long ago as 100 million years, and there are clear 
examples of seagrass fossils from the Cretaceous. 
Further studies have failed to produce evidence of any 
massive diversification or of major extinction events, 
and so it may be that seagrasses have simply followed 
a relatively conservative evolutionary pathway. More 
work is required in this field". 


Seagrasses do not grow in isolation but form an 
integral and often defining part of highly complex 
ecosystems. The seagrasses themselves are an 
important standing stock of organic matter, which is 
relatively stable in the tropics and has broad intra- 
annual variation in temperate regions. The productivity 
of these ecosystems is usually enhanced by other 
primary producers, including macroalgae and epiphytic 
algae. The abundant plant material of seagrass beds 
forms an integral part of many food chains. 
Additionally, the complex three-dimensional structure 
of the seagrass bed is important, providing shelter and 
cover, binding sediments and, at fine scales, even 
altering the patterns and strength of currents in the 
water. The complex, modified seagrass environment 
provides a great variety of niche spaces on and within 
the sediments, on the plant surfaces and within the 
water column. 

Thus, despite the relatively small number of 
seagrass species, a vast array of other species can be 
found within seagrass ecosystems. Many are obligate 
members of the seagrass ecosystem, found nowhere 
else. Others may be restricted to seagrass areas for 
shorter periods of their life histories, using them as 
breeding or nursery areas, or settling there for their 
adult lives. Many more are found across a broad range 
of marine habitats, but regularly inhabit seagrass 
areas. Table 2 provides a list of some of the major 
taxonomic groups typically associated with seagrass 

Seagrass ecosystems often play an important 
role in the functioning of a wider suite of coastal and 
marine ecosystems, including coral reefs and man- 
groves in the tropics, but also soft muddy bottoms, 
intertidal flats, salt marshes, oyster reefs and even 
pelagic ecosystems. 

Levels of species diversity in seagrass eco- 
systems can be very high indeed. Humm'” listed 113 
species of algal epiphytes from Thalassia testudinum 
beds in Florida. Using this, combined with lists from 
26 other publications worldwide, Harlin” produced a 
list of some 450 algal species that are epiphytic 

The distribution and status of seagrasses 

Overview Table 2 
Major taxonomic groups found in seagrass ecosystems, with brief notes 
Taxonomic group Notes 


Fungi Including Plasmodiophora 
Diatoms (Bacillariophyta] 
Blue-green algae (Cyanophyta] 
Red algae (Rhodophyta) 

Brown algae (Phyaeophyta] 
Green algae (Chlorophyta) 

Including calcareous species 
Including Padina 
Notably Ulva, Halimeda and Caulerpa 


Ribbon worms 
Sipunculid worms 

Bivalve mollusks 
Gastropod mollusks 
Cephalopod mollusks 



Includes the slime molds Labyrinthula spp., and Foraminifera 

Includes epiphytic and free-standing species 

Includes epiphytic hydrozoans, sea anemones, solitary corals and Scleractinia such as Pavona, 
Psammacora, Porites, Pocillopora, Siderastrea 

Including rag-worms (nereids) 

Includes amphipods, and many decapod crustaceans including crabs, stomatopods and commercially 
important shrimp and lobster 

Some oysters and scallops, also many boring species 

A broad range including Conus, Cypraea and commercially important species of Strombus 

Squid and cuttlefish often found over seagrass areas 

Epiphytic on seagrass and rocks 

A range of commercially important holothurian species, ophiroids are widespread, but also asteroids and 


All groups, but including the commercially important Haemulidae (grunts), Siganidae (rabbitfish), 
Lethrinidae {emperors}, Lutjanidae [snappers], Bothidae (left-eye flounders), Syngnathidae (pipefishes and 
sea horses]; many of the latter, which are used in the aquarium trade and Chinese medicine trade, are 

considered threatened 
Notably the green turtle Chelonia mydas 
Notably brant (geese) and other migrating waterfowl and wading birds 


Source: Key references for this table include various chapters in Phillips and McRoy 


on seagrasses, still probably an underestimate. 
Hutchings" listed some 248 arthropods, 197 mollusks, 
171 polychaetes and 15 echinoderm species from 
Jervis Bay in New South Wales, Australia. In Florida, 
Roblee et al.” noted 100 species of fish and 30 species 
of crustaceans in seagrass beds. 

A number of studies have compared diversity in 
seagrass beds with that observed in adjacent eco- 
systems. Seagrasses consistently have higher levels of 
diversity than adjacent non-vegetated surfaces; how- 
ever, if other vegetated surfaces, or coral reefs, are 
compared these often have similar to significantly 

higher levels of diversity”. 

Notably the sirenian species dugong Dugong dugon and manatee Trichechus manatus, Trichechus 

('8| and review comments by the contributors to this World 

Despite this high diversity and the importance of 
associated species, there is no detailed database of 
species associated with seagrass beds. Many of the 
species that have been recorded are also found in other 
ecosystems, although some appear to be restricted to 
seagrass ecosystems or dependent on them for at least 
a part of their life cycles. Such seagrass-dependent 
species range from particular epiphytic algae” to the 
large seagrass-grazing manatee and dugong. Most of 
the comprehensive faunal assessments have been 
undertaken in temperate waters, or the relatively low- 
diversity waters of the Caribbean, and it seems likely 
that further work in the Indo-Pacific in particular will 



lead to large increases in the recorded numbers of 
seagrass associates. 

Threatened and restricted range species 

Within the wider conservation arena, species with 
restricted distributions, together with threatened 
species, are often singled out for attention. Apart from 
concerns over these individual species, they are often 
used as “flagship species” to draw attention to partic- 
ular areas and issues. Amongst the seagrasses, 
however, the problems of taxonomic uncertainty under- 
mine the determination of both threat and restricted 

Two species of seagrass have been listed as 
threatened by IUCN-The World Conservation Union'*” 
{see Table 3): Halophila johnsonii and Phyllospadix 
serrulatus. A number of countries harbor the sole 
populations of a seagrass species (national endemics}, 
most notable of which is Australia, with 13 species 
found nowhere else in the world. Such national 
endemism has no inherent ecological significance, 
although it can be used as a basis to support 

Overview Table 3 

conservation actions. Using the species range maps, it 
is possible to calculate the total area of each species 
range. For such calculations it was necessary to modify 
the broad range maps and not to include areas outside 
the continental shelf in the calculations. These range- 
area Statistics are provided next to the species range 
maps in Appendix 3. From this work we can see that only 
a small number of species have truly restricted ranges, 
notably: Halodule bermudensis (1000 km’), Halophila 
hawaiiana (7000 km’), Halophila johnsonii (12000 km’), 
Posidonia ostenfeldii (66000 km’), Posidonia kirkmanii 
(66000 km’) and Halodule beaudettei (74000 km’). 
However, all these six species are in the process 
of taxonomic review and their individual species 
designations are presently in question. 

Given the problems of taxonomy, and the low 
threat to the existence of individual seagrass species, 
measures of restricted range, endemism or threat of 
extinction are probably of little value in seagrass 
conservation efforts. Similar arguments are not true for 
seagrass-associated animals, although here lack of 
knowledge hampers a true assessment of the full 

Threatened species regularly recorded from seagrass communities worldwide 

Common name Status 
Johnson's seagrass 

Surf grass 

Horseshoe crab 
Horseshoe crab 
Big-bellied sea horse 
Sea horse 

Short-headed sea horse 
Lined sea horse 

Sea pony 

Spiny or thorny sea horse 
Sea horse 


Halophila johnsonii 
Phyllospadix serrulatus 
Carcinoscorpius rotundicauda 
Tachypleus tridentatus 
Hippocampus abdominalis 
Hippocampus borboniensis 
Hippocampus breviceps 
Hippocampus erectus 
Hippocampus fuscus 
Hippocampus histrix 
Hippocampus jayakari 

* Juveniles regularly observed in seagrass beds. 

Common name Status 
Spotted or yellow sea horse Vu 
Slender sea horse Vu 
White's sea horse Vu 
Dwarf sea horse Vu 
Nassau grouper En 
Venezuelan grouper Vu 
Gag grouper Vu 
Green turtle En 
Dugong Vu 
West Indian manatee Vu 
West African manatee Vu 


Hippocampus kuda 
Hippocampus reidi 
Hippocampus whitei 
Hippocampus zosterae 
Epinephelus striatus* 
Mycteroperca cidi* 
Mycteroperca microlepis* 
Chelonia mydas 

Dugong dugon 
Trichechus manatus 
Trichechus senegalensis 

This list includes only species which are partially or wholly dependent on seagrasses and may be incomplete. 
DD - Data Deficient: A taxon is Data Deficient when there is inadequate information to make a direct, or indirect, assessment of its risk of 
extinction based on its distribution and/or population status. A taxon in this category may be well studied, and its biology well known, but 

appropriate data on abundance and/or distribution is lacking. 

R - Rare: Taxa with small world populations that are not at present Endangered or Vulnerable but are at risk. These taxa are usually localized 
within restricted geographic areas or habitats or are thinly scattered over a more extensive range 
Vu - Vulnerable: A taxon is Vulnerable when it is not Critically Endangered or Endangered but is facing a high risk of extinction in the wild in the 

medium-term future. 

En - Endangered: A taxon is Endangered when it is not Critically Endangered but facing a very high risk of extinction in the wild in the near future. 
Critically Endangered: A taxon is Critically Endangered when it is facing an extremely high risk of extinction in the wild in the immediate future. 

Source: Walter and Gillett'2!. |UCN!4, 

threats facing many species. Table 3 provides a list of 
some of the known seagrass species and seagrass 
associates listed as threatened by IUCN". The clear 
focus of this list towards a few groups is probably 
indicative of the general lack of knowledge of the status 
of many seagrass associates. This problem has also 
been more widely recognized by IUCN! which 
acknowledges that “there has been no systematic 
assessment” apart from some limited groups. Of the 
species which have been listed, most remain poorly 
known or are ranked at a relatively low level of threat 
such as “Vulnerable”. 


The known locations of seagrass ecosystems, based 
on the mapping efforts described above, are presented 
in the World Seagrass Distribution Map {Map 1) and in 
the maps which appear in Chapters 1-24. In some 
parts of the world, notably the western North Atlantic, 
the Gulf of Mexico, Queensland [Australia], Western 
Australia and some parts of the Mediterranean, the 
maps are based on fairly comprehensive information 
on seagrass distribution. Elsewhere, available 
information is more sporadic, restricted to individual 
sites, bays or national coverages for smaller countries, 
though there may be some documentation of broader 
distribution patterns. Typically this is the case for 
areas such as the western Pacific, the Indian Ocean 
and the Caribbean. Over a few large stretches of the 
world’s coasts, there exists almost no information on 
whether or not seagrasses occur, let alone their 
density, extent or species composition. This is notably 
the case for West Africa, South America, Greenland, 
northern China and the Siberian coast, and parts of 
Southeast Asia and the Pacific islands. 

The World Seagrass Distribution Map shows the 
broad distribution of seagrasses in most of the world’s 
oceans and seas, including the Black, Caspian and Aral 
Seas, and further shows the considerable latitudinal 
range of seagrasses. The most northerly locations for 
seagrasses are for Zostera marina which is recorded at 
Veranger fjord in Norway at 70°30'N, Chéshskaya Guba 
in Russia (67°30'N) and in Alaska [at 66°33’N). The 
most southerly locations are for Zostera capricorni in 
New Zealand, with the southernmost record being at 
46°55'S on Stewart Island, and Ruppia maritima in the 
Straits of Magellan (54°S). 

A limitation of these distribution maps is that 
they provide no information on the extent of coast- 
lines surveyed without finding seagrass and hence do 
not distinguish between “no seagrass” and “no 
information". Gaps in the distribution maps may 
result from the lack of available data for certain parts 
of the world, but in other areas they reflect knowledge 
that no seagrass exists. Thus the western coastlines 

The distribution and status of seagrasses 

A sea horse, Hippocampus kuda, among Enhalus acoroides, 

southern Peninsular Malaysia 

of South America and of much of West Africa may 
indeed have more seagrass communities than are 
reflected here. 


The calculation of a global seagrass habitat area is very 
important and useful for an assessment of the role of 
seagrasses in global processes, particularly in global 
carbon budgets, and also in assessing historical and 
future loss of seagrass and in priority setting and 
management of natural resources for activities such as 
fisheries and conservation. 

To date the only global area estimate for 
seagrasses has been one of some 600000 km?” 
reportedly derived from Charpy-Roubaud and 
Sournia””. The latter paper, however, does not provide 
an area estimate directly, and it would appear that the 
figure of 600000 km’ is derived from a global estimate 
of seagrass productivity’ *” and typical seagrass 
productivity figures taken from an unspecified source. 
This estimate’ seems too large, as the original source 
of global productivity was itself based on an area 
estimate of only 350000 km’ for seagrasses, salt 
marshes and mangrove communities combined. 

The calculation of global and regional habitat 
areas for the marine environment can be done using 
two broad approaches. The first is to estimate or model 
probable habitat area utilizing known and mapped 
parameters, such as bathymetry, coastal features or 
existing biogeographic knowledge. The second involves 


Overview Table 4 
Estimates of seagrass coverage for selected areas 
described in this World Atlas 

Location Area (km?} 
Scandinavia 1850 
Western Europe 338 
Western Mediterranean 4152 
Euro-Asian Seas 2600 
Saudi Arabia 



Western Australia 

Eastern Australia 

New Zealand 


Peninsular Malaysia 

Kosrae, Federated 

States of Micronesia 



Viet Nam 


Korea, Republic of 

Pacific coast of North America 1000 
Western North 374 
Atlantic coast of USA 

Mid-Atlantic coast 292 
of USA 

Gulf of Mexico 19349 
East coast of Florida 2 800 
Mexico 500 
Belize 1500 





Grand Cayman 





Note: Almost certainly an underestimate in most cases. 

the use of mapped data to develop a more direct 
calculation. In many studies, elements of both 
approaches have been combined. 

Using a simple modeling approach, the total area 
of continental shelf (coastal waters to a depth of 200 m) 
worldwide has been estimated at almost 25 million 
km?" Assuming a constant slope, this estimate would 
imply an area of approximately 5 million km? of benthos 

Average area 






N Hectares 

Overview Figure 1 
Relative size-frequency distribution of 538 seagrass polygons in 
latitudinal swathe 20-30°S 

Notes: The number of polygons is plotted on the primary y-axis [bars] 
against a logarithmic scale of area. The percentage frequency of each size 
class is plotted on the secondary y-axis [dots] and the mean area of all 
polygons in each size category is stated at the top of the columns. In this 
swathe there are 180 seagrass polygons of 1-10 ha in area. In other words 
33 percent of the polygons in this swathe have an average area of 4.84 ha 
In the area calculation it was therefore assumed that a third of all points at 
these latitudes were each representative of a seagrass area 4.84 ha in size, 
that 37 percent of points were representative of areas 35.7 ha in size, etc. 

within the depth range of most seagrasses, although 
for large parts of the globe turbidity, substrate 
characteristics and other factors reduce this area of 
potential seagrass. In reality, seagrasses occupy only a 
fraction of the world’s nearshore waters. If the total 
area of seagrasses is less than 10 percent of the 
shallow water area of the world’s continental shelves, 
then the maximum area would be 500000 km’. This 
upper limit incorporates many assumptions and is 
likely to be an overestimate. 

Many of the authors of the subregional and 
national chapters of this World Atlas of Seagrasses 
have either summarized the existing seagrass maps for 
their area or consulted expert opinion to produce 
estimates of seagrass coverage. Further details are 
provided in the relevant chapters but these totals are 
summarized in Table 4. 

These chapters document some 164000 km’? of 
seagrass but as these cover a limited geographic area 
and a subset of known locations they cannot be used to 
generate a global area. 

The World Seagrass Distribution Map, developed 

ona GIS, is now the most comprehensive map of global 
seagrass occurrence in existence. Using this we have 
begun to explore the direct calculation of global 
seagrass area. 

The World Seagrass Distribution Map dataset 
includes more than 37000 polygons and some 8800 
points. A total area of 124000 km‘ is clearly defined by 
the polygons but these provide only partial geographic 
coverage from a few areas which tend to be well known. 
Point data represent seagrass areas where habitat 
maps are not available. Though more poorly known 

The distribution and status of seagrasses 

large and important seagrass meadows and should be 
factored into any calculation of area. We have 
experimented with methods of using the polygon data 
to estimate the seagrass area of these points by 
calculating logarithmic size-frequency distributions of 
polygon data in 10-degree latitudinal swathes. 
The distribution was then applied to the points within 
the swathe, generating an estimate for total seagrass 
area (Figure 1}. Very small polygons, from data derived 
from remote sensing (these small polygons tend to be 
single or clusters of few pixels), and very large 

than mapped areas, these locations are likely to have polygons, derived from sketch maps covering 

Overview Table 5 
Functions and values of seagrass from the wider ecosystem perspective 

Function Ecosystem values 

Primary production - including Seagrasses are highly productive, and play a critical role as food for many herbivores (manatee, dugong, 

benthic and epibenthic production turtles, fish, waterfowl, etc.]. This productivity lies at the base of the food chain and is also exported to 
adjacent ecosytems. 

Canopy structure The growing structures of seagrasses provide a complex three-dimensional environment, used as a 

habitat, refuge and nursery for numerous species, including commercially important fish and shellfish. 

Epiphyte and epifaunal substratum The large surface area of seagrass above-ground biomass provides additional space for epiphytes and 
epifauna,-supporting high secondary productivity. 

Nutrient and contaminant filtration Seagrasses help to both settle and remove contaminants from the water column and sediments, improving 
water quality in the immediate environment and adjacent habitats. 

Sediment filtration and trapping — The canopy of seagrasses helps to encourage settlement of sediments and prevent resuspension, while 
the root systems help to bind sediments over the longer term, improving water quality and in some places 
helping to counter sea-level rise. 

Creating below-ground structure The complex and often deep structures of the seagrass roots and rhizomes support overall productivity 
and play a critical role in binding sediments. 

Oxygen production The oxygen released from photosynthesis helps improve water quality and support faunal communities in 

seagrasses and adjacent habitats. 

Many seagrass ecosystems are net exporters of organic materials, supporting estuarine and offshore 


Seagrasses hold nutrients in a relatively stable environment, and nutrient recycling can be relatively 

Organic production and export 

Nutrient regeneration and 
recycling efficient, supporting overall ecosystem productivity. 

Organic matter accumulation Along with sediments the organic matter of roots, rhizomes and even leaves can remain bound within the 
sediment matrix, or accumulate on adjacent coastlines or other habitats, building up the level of the 
benthos and supporting other food webs. 

By holding and binding sediments, and by preventing the scouring action of waves directly on 

the benthos, seagrasses dampen the effects of wave and current energy, reduce processes of erosion, 
reduce turbidity and increase sedimentation. 

Seagrasses are capable of both self-maintenance and spreading to new areas via sexual and asexual 
reproduction. Recovery following storms, disease or human-induced damage can be relatively rapid. 

The complex community of the seagrass ecosystem supports important biodiversity and provides trophic 
interactions with other important ecosystems such as coral reefs, mangroves, salt marshes and shellfish 

Wave and current energy 

Seed production/vegetative 
Self-sustaining ecosystem 

As perennial structures, seagrasses are one of the few marine ecosystems which store carbon for 
relatively long periods. In a few places such carbon may be bound into sediments or transported into the 

Carbon sequestration 

deeper oceans and thus play an important role in long-term carbon sequestration. 

Source: Derived from Short et al'*"’ and Global Seagrass Workshop recommendations. 


Overview Table 6 

Summary of the goods and services provided by seagrass 

Commercial and artisanal fisheries’ 

Finfish (snappers, emperors, rabbitfish, surgeonfish, 

Mollusks (conch, oysters, mussels, scallops, clams)’ 
Crustacea (shrimp, lobster, crab] 

Mammals and reptiles (dugongs, manatee, green turtle} ”” 

Nursery habitat for offshore fisheries” ™ 

Seeds of Zostera marina used to make flour by Seri Indians” 
Rhizomes of Enhalus used as food in Lamu, Kenya” 

Fodder or bedding for animals" “” 


Used in mat weaving, Lamu, Kenya” 

Basket making, thatch, stuffing mattresses, upholstery“ 

Packing material” 

Fertilizer and mulch“ 

Building dikes“ 

Coastal protection from erosion” *” 

Water purification 

Reducing eutrophication and phytoplankton blooms” 
Removing toxic organic compounds from water column and 

Interaction with adjacent ecosystems” 

Nutrient export 

Source of food or shelter, as a nursery, resting ground or 
feeding ground” 

Water column filtration™ 

Maintenance of biodiversity and threatened species” 
Dugongs, manatee, green turtle” 

Carbon dioxide sink’ 

Cultural, esthetic and intrinsic values“ 
Places of natural beauty 

Recreational value 

Educational value 

Stabilizing sediments 

Binding function of roots 

Role of shoots in reducing surface flow and encouraging 

Source: Various sources - see references by entries 

enormous areas [e.g. the global National Geographic 
“Coral World” map], were excluded from this analysis 
to avoid serious under- and overestimates respectively. 

When combined with polygon data this method 
generates an estimate for the global coverage of 
seagrass of 177000 km’ (using median polygon areas 
reduced the estimate by 4 percent). It is based on the 
most comprehensive dataset on seagrass distribution 
to date. However it is necessarily and unavoidably 
based upon a number of crude assumptions and is 
intended to be no more than indicative of the global 
extent of seagrass. In any event, even the 177000 km’ 
is an underestimate of the actual global seagrass area, 
since for many areas seagrasses have not been 
documented. Until our knowledge of seagrasses in 
large areas such as insular Southeast Asia, the east 
coast of South America and the west coast of Africa 
improves, it is unlikely that a better estimate can 
be generated. 


Seagrasses are a critical ecosystem: their role in 
fisheries production, and in sediment accumulation 
and stabilization, is well documented, but there are 
many other important roles, both in terms of their place 
in the ecosystem and their value to humanity. Table 5 
lists a number of the functions of seagrasses from a 
wider ecosystem perspective. 

Seagrasses have a relatively low biomass 
compared with terrestrial ecosystems, but have a very 
high biomass in relation to planktonic-based marine 
communities. Figures for average biomass vary 
considerably between seagrass species and between 
studies; communities of Amphibolis, Phyllospadix and 
Posidonia in particular are noted for their high 
biomass, the last’s enhanced by extensive stem and 
root systems. In contrast, species of Halophila, with 
their small petiolate leaves and high turnover rates, 
rarely achieve high biomass. 

Duarte and Chiscano’, in a literature review, 
calculated from nearly 400 samples an average 
biomass for different seagrass species, and by 
averaging these values derived an average biomass for 
seagrass of 460 g dry weight/m’ {above- and below- 
ground biomass combined]. As an estimate of global 
seagrass biomass, such estimates are biased towards 
large seagrass species. Taking these factors into 
account, the median biomass statistic of 205 g dry 
weight/m’, also from data in Duarte and Chiscano, may 
be a more accurate reflection of the typical biomass for 
seagrass communities worldwide. 

In terms of productivity, Duarte and Chiscano 
estimated an average net primary production of about 
1012 g dry weight/m’/year. Even allowing for 
overestimation, such figures are very high for marine 


communities, with the same source citing productivity 
figures for macroalgal communities of 1 g dry 
weight/m’/day and of phytoplankton of 0.35 g dry 

The high productivity and biomass of seagrasses 
are an integral part of many of their uses and values 
from a human perspective. A broad sample of the 
goods and services provided by seagrasses is shown in 
Table 6, while further information on a number of these 
is given in the text, both here and in many of the 
regional and national chapters. 


Seagrass ecosystems are highly productive and also 
have a relatively complex physical structure, thus 
providing a combination of food and shelter that enables 
a high biomass and productivity of commercially 
important fish species to be maintained” °”. Seagrasses 
also provide an important nursery area for many 
species utilized in offshore fisheries and in adjacent 
habitats such as coral reefs and mangrove forests. In 
most cases, the association between commercially 
important species and seagrasses Is not obligatory; the 
same species are found in other shallow marine 
habitats. There are, however, a number of studies which 
clearly show the higher biomass of such species 
associated with seagrasses as compared with adjacent 

unvegetated areas”. 

Sediment stabilization and coastal protection 

Seagrasses are the only submerged marine photo- 
trophs with an underground root and rhizome system. 
This below-ground biomass is often equal to that of the 
above-ground biomass, and can be considerably more 
e.g. Posidonia’. The role of these roots and rhizomes in 
binding sediments is highly important, as has been 
illustrated in a number of studies that have compared 
erosion on vegetated versus non-vegetated areas 
during storm events. The role of seagrass shoots in this 
process is also important, as these provide a stable 
surface layer above the benthos, baffling currents and 
therefore encouraging the settlement of sediments and 

inhibiting their resuspension”. 

Water purification and nutrient cycling 

By enhancing processes of sedimentation, and through 
the relatively rapid uptake of nutrients both by 
seagrasses and their epiphytes, seagrass ecosystems 
remove nutrients from the water column. Once 
removed these nutrients can be released only slowly 
through a process of decomposition and consumption, 
quite different from the rapid turnover observed in 
phytoplankton-dominated systems. In this way 
seagrasses can reduce problems of eutrophication and 

bind organic pollutants”. 

The distribution and status of seagrasses 

Mitigating climate change 

The role of the world’s oceans in removing carbon 
dioxide from the atmosphere is still being investigated 
and remains poorly understood. It appears that 
biological processes in the surface layers of the world’s 
oceans are one of the few mechanisms actively 
removing carbon dioxide from the global carbon 
cycle. Within these processes, seagrasses clearly 
have a minor role to play, although their high 
productivity gives them a disproportionate influence on 
primary productivity in the global oceans on a unit area 
basis, and they typically produce considerably more 
organic carbon than the seagrass ecosystem 
requires’. Any removal of carbon either through 
binding of organic material into the sediments or 
export into the deep waters off the continental shelf 
represents effective removal of carbon dioxide from the 
ocean-atmosphere system which could play some role 
in the amelioration of climate change impacts. 

Maintaining biodiversity and threatened species 

The concept of seagrasses as high-diversity marine 
ecosystems has often been overlooked, but this role 
has already been briefly outlined above. Seagrasses 
also play a role in safeguarding a number of threatened 
species, including those such as sirenians, turtles and 
sea horses, which are widely perceived to have very 
high cultural, esthetic or intrinsic values by particular 
groups. The wider functions of biodiversity include the 
maintenance of genetic variability, with potential 
biochemical utility, and a possible, though poorly 
understood, role in supporting ecosystem function and 

Economic valuation 

There have been very few studies of the direct 
economic value of seagrasses. In Monroe County, 
Florida, the value of commercial fisheries for five 
species which depend on seagrasses was estimated at 
US$48.7 million per year, whilst recreational fisheries, 
as well as the diving and snorkeling industry in that 
county, contribute large sums to the economy and are 
also indirectly dependent on seagrasses”. 

Costanza et al.’ calculated a global value of 
annual ecosystem services for “seagrass/algae beds” 
of US$19004 per hectare per year. With their estim- 
ated total area for these combined ecosystems of 
2000000 km’ they calculated a global annual value of 
US$3 801000000000 [i.e. US$3.8 trillion], based 
almost entirely on their role in “nutrient cycling”, 
which is only one of many values of the ecosystem. The 
same source gives no value to seagrass/algae beds for 
food production. 

Further information is needed to demonstrate the 
full economic value of seagrass ecosystems worldwide. 



Damage to seagrass beds caused by yachts in Jersey, Channel 
Islands, UK 

It will be important not only to measure direct value 
from activities such as fisheries but also indirect values 
associated with various functions {Table 5] including 
maintenance of water quality and protecting coastlines. 
In many ways dollar values provide only a part of the 
true picture of the value of an ecosystem, and it Is 
important to consider other possible means to quantify 
value, including employment, protein supply or even 
quality of life as alternative measures which address 
value from a human perspective. It should be noted that 
even when dollar values are estimated they do not 
represent the entire worth of the ecosystem and in no 
way constitute a purchase value. 


The global threats to seagrasses have received 
considerable attention from a number of authors [e.g. 
Short et al”, Phillips and Durako'”, Short and Wyllie- 
Echeverria’, Hemminga and Duarte’) and their 
efforts are only summarized here. In many cases it 
seems likely that declines in seagrass areas have been 
the result not of individual threats but a combination of 
impacts. Typical combined impacts may include in- 
creased turbidity, increased nutrient loads and direct 
mechanical damage. Seagrasses exist at the land-sea 
margin and are highly vulnerable to the world’s human 

populations which live disproportionately along the 
coasts. Such conditions threaten seagrass ecosystems 
and have resulted in substantial loss of many seagrass 
areas in the more populated parts of the world, as well 
as degradation of much wider areas over the last 
100 years. 

A number of natural threats to seagrasses have 
been recorded. Geological impacts may include 
coastal uplift or subsidence, raising or lowering beds 
to less than ideal growing conditions. Meteorological 
impacts can also affect seagrasses: major storm 
events in particular may remove surface biomass and 
even uproot and erode wide areas of shallow water. 
Finally there are biological impacts. Typically these 
are part of the ongoing processes in seagrass 
ecosystems, such as grazing by fish, sea urchins, 
sirenians, geese or turtles; they also include 
disruption to the sediments by burrowing animals or 
foraging species such as rays. It is rare that such 
activities should disrupt seagrass beds over large 
areas. Diseases, however, represent an important 
biological impact which can have very widespread 
effects. The eelgrass wasting disease recorded from 
the North Atlantic in the 1930s" *” was caused by the 
slime mold Labyrinthula zosterae”*”. This wasting 
disease continues to occur and remains a threat to 
eelgrass in the North Atlantic!” Similarly in Florida 
Bay, disease caused by Labyrinthula sp. has been 
implicated in an extensive seagrass die-off'". 

Human threats to seagrasses are now 
widespread. Many result in direct destruction of these 
habitats. Dredging to develop or widen shipping lanes 
and open new ports and harbors, and certain types of 
fishery such as benthic trawling, have led to losses of 
wide areas of seagrass. Boating activities frequently 
lead to propeller damage, groundings or anchor 
damage, often increasing sediment resuspension or 
creating holes and initiating “blow-out" areas in 
seagrass beds. Construction activities within coastal 
waters have sometimes led to losses: land reclamation 
is aclear example, as is the construction of aquaculture 
ponds in some areas. Even the construction of docks 
and piers can lead to some direct losses, and to further 
losses arising from shading or fragmentation of 
seagrass beds. The alteration of the hydrological 
regime as a result of coastal development and the 
building of sea defenses can also impact seagrasses. 
There are examples of direct and deliberate removal of 
seagrasses, for example to “clean” tourist beaches or 
to maintain navigation channels. 

In addition, many seagrass beds have been 
affected by the indirect impacts of human activities. 
Land-based threats include increases of sediment 
loads: higher turbidity reduces light levels, while very 
high sedimentation smothers entire seagrass beds. 

Similarly, while seagrasses can assimilate certain 
levels of nutrient and toxic pollutants, high levels of 
increased nutrients from sewage disposal, overland 
runoff and enriched groundwater discharge can reduce 
seagrass photosynthesis by excess epiphytic over- 
growth, planktonic blooms or competition from 
macroalgae. Toxins can poison and kill seagrasses 
rapidly. Another indirect threat comes from the 
introduction of alien or exotic species. The alga 

Overview Table 7 
Summary of marine protected areas [MPAs] that contain seagrass ecosystems, from the UNEP-WCMC Protected Areas Database 

Country or territory Number of sites 

Antigua and Barbuda 





British Indian Ocean Territory 


Cayman Islands 


Costa Rica 




Dominican Republic 

French Polynesia 









Korea, Republic of 


The distribution and status of seagrasses 

Caulerpa taxifolia, released into the Mediterranean in 
the 1980s, has smothered and killed wide areas of 
seagrass beds. In 1999, the same species was first 
observed off the coast of California and could have the 
same impact there”. 

Climate change represents a relatively new threat, 
the impacts of which on seagrasses are largely 
undetermined“. Potential threats from climate change 
may come from rising sea levels, changing tidal 

Country or territory Number of sites 
Monaco i 

Netherlands Antilles 



Papua New Guinea 

Puerto Rico 


Russian Federation 

Saint Lucia 

Saint Vincent and the Grenadines 
Saudi Arabia 




South Africa 





Trinidad and Tobago 


Turks and Caicos Islands 

United Kingdom 

United States 

United States minor outlying island 

Viet Nam 

Virgin Islands (British) 

Virgin Islands (US) 

OF SS Sw nM — WwW Oe DY OW — — — LY OC 

Note: Few of these sites are managed directly to support seagrass 
protection, and in many cases they do not protect the most 
important areas of seagrass In a region. 



regimes, localized decreases in salinity, damage from 
ultraviolet radiation, and unpredictable impacts from 
changes in the distribution and intensity of extreme 
events. In contrast there could be increases in 
productivity resulting from higher carbon dioxide 

Various studies have attempted to quantify the 
decline of seagrasses, although it must be accepted 
that seagrasses have been degraded or lost over vast 
areas without any knowledge of their existence. Short 
and Wyllie-Echeverria’””” provide an analysis of 
seagrass losses from reports worldwide. They found 
that a loss of 2900 km’ of seagrass was documented 
between the mid-1980s and the mid-1990s, and they 
extrapolated likely seagrass losses over that time 
period alone of up to 12000 km’ worldwide. 


The dramatic and accelerating declines in seagrass 
areas worldwide are mirrored in other coastal 
ecosystems such as mangroves and coral reefs”. 
Concerns about these declines have prompted some 
increase in efforts to protect these ecosystems. 
Perhaps the most valuable protection measure is the 
wholesale reduction of the full suite of anthropogenic 
impacts via legislation and enforcement at local and 

—— Number of sites 

200 (left-hand scale) 

~~ il Total area protected, 
thousand km 
(right-hand scale] 


1900 10 20 30 40 50 60 70 80 90 2002 

Overview Figure 2 

Growth of marine protected areas which include seagrass 
ecosystems, shown both as the number of sites (line] and the total 
area protected (shaded area] 

Notes: The total area statistics are for the entire MPAs; there is no 
information on the area of seagrass within these sites but it Is likely to be 
only a small fraction of the total area. Figure 2 covers only those sites for 
which a date of designation has been recorded. In addition to the 205 sites 
shown here there are a further 42 with a total area of some 3 500 km? 
whose year of designation is not known 

regional scales. Unfortunately the cost is high and rates 
of improvement are low. 

More practical protection, although only localized 
in effect, is the establishment of marine protected 
areas [MPAs], legally gazetted sites where certain (but 
by no means all) human activities are controlled or 
prohibited in order to provide some protection of 
marine resources or to promote sustainable fisheries. 
Whether out of direct interest or as an indirect 
beneficiary, seagrass habitat is present in an 
increasing number of sites in the expanding MPA 
network. The total number of MPAs has increased 
dramatically in recent years, from less than 500 MPAs 
worldwide in 1960 to more than 4000 by 2001 (UNEP- 
WCMC data, but note that this figure includes intertidal 
as well as subtidal sites}. No MPAs have been 
designated solely for the protection of seagrasses; 
however seagrasses are often one of a list of key 
habitats singled out when sites are recommended for 
protection [e.g. the Great Barrier Reef Marine Park in 
Australia]. Many other sites include seagrasses even 
when the key natural resource behind their protection 
may be something else, such as a coral reef. In the 
majority of MPAs, seagrasses are not acknowledged or 
directly protected. With increased awareness, MPA 
boundaries and protection could be expanded to 
incorporate adjacent seagrass habitats (e.g. Florida 
Bay adjacent to the Everglades). 

UNEP-WCMC maintains a global database on 
MPAs on behalf of the IUCN World Commission on 
Protected Areas. Linked to the current work, a list of 
the areas which are known to contain seagrass habitat 
has been prepared and is presented in Appendix 2. A 
summary of this information is provided in Table 7. 

Worldwide there are some 247 MPAs known to 
include seagrasses. These are located in 72 countries 
and territories. These numbers are likely to be 
conservative: seagrasses may well occur at a site but 
not be recorded, or not be listed in literature which 
has been used to develop this database. Even so, it 
seems likely that this list is far smaller than the 
equivalent network for coral reefs {more than 660") 
and mangrove forests {over 1800, unpublished data 
2000) and clearly does not present any form of global 
network. Added to this must be the recognition that 
the vast majority of these sites do not provide any 
clear protection for seagrasses - their inclusion 
within MPAs is largely fortuitous. 

Figure 2 shows the increase in seagrass MPAs 
over the past century. It should be noted that the area 
figures (shaded area) are a measure of the total area 
covered by these MPAs. At the present time it is 
impossible to determine the area of seagrasses within 
these sites, although it is likely to be only a very small 
fraction of the total area. It should further be noted that 


The distribution and status of seagrasses 

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designation as “protected” covers a broad range of 
types of protection, both in terms of legal status and 
practical application of that status. Some sites, such as 
the National Estuarine Research Reserves in the 
United States, do not provide any direct habitat 
protection under their supporting legislation. In many 
other cases, even where the legislation may provide a 
formal safeguard, management may be inadequate. 
The world’s largest MPA, Australia’s Great Barrier Reef 
Marine Park, has made some efforts to prevent 
trawling in seagrass areas, but this entire park, like 
most others worldwide, is still subject to influences 
from beyond the park boundaries. 

In a recent analysis by regional experts, manage- 
ment effectiveness was considered for some 342 MPAs 
in Southeast Asia and was rated as “good” for only 46 
sites (14 percent)’. Finally, many of the threats facing 
seagrasses come from remote sources, notably terres- 
trial runoff. Few protected areas currently manage 
entire watersheds and the legal framework is typically 
powerless to control nutrient and toxic pollution and 
sedimentation arising outside an MPA. 

In addition to the designation of MPAs, other legal 
measures have proved beneficial to seagrasses in some 
places, although seagrasses themselves are rarely 
singled out as the object of protection. Such legislation 
includes restrictions on particular activities such as 
trawling, dredging or the release of land-based sources 
of degradation such as sediments and pollutants. For 
example, in Queensland waters (Australia) all sea- 
grasses and other marine plants are specifically 
protected under the Fisheries Act of 1994, for the 
protection of commercial and recreational fishing 
activities. In South Australia seagrass is protected 
under the Native Vegetation Act 1992. In the United 
States, seagrass habitats are protected under Section 
404(c) of the Clean Water Act from direct dredge and fill 
activities without a permit’. Although clearly 
important, such legislation is rare, and still insignificant 
at the global level. 

In addition to legal protection, public education 
can play an important role in safeguarding seagrasses, 
notably via the protection of charismatic seagrass 
associates such as turtles and dugongs, but also in the 
directing of activities which could impact seagrasses. 
Coles and Fortes’ provide a valuable review of 
methods for direct and indirect protection of 

Seagrass restoration may include both the 
improvement of overall conditions for seagrass growth 
in an area, such as an improvement in water clarity 
resulting from decreased runoff or nutrient inputs, as 
wellas direct transplanting or seeding of seagrasses”. 
Sometimes transplanting is mandated as mitigation for 
unavoidable damage to seagrasses incurred in coastal 

The distribution and status of seagrasses 

The shallow seagrass beds of Montepuez Bay, Mozambique, at low 

development. Transplanting cannot be successful 
unless the conditions for seagrass to thrive pre-exist’””. 
Although widely undertaken in some areas, many 
transplantation efforts have had low success rates and 
transplanting can be quite labor intensive and ex- 
pensive”. Technologies for more uniformly successful 
and less expensive seagrass transplanting are evolving, 
and include developing models for site selection”, 
advanced methods for transplanting” and seeding”, 
and scientific success criteria’. Restoration of 
seagrasses is now at the stage where technologies are 
available, but overcoming insufficient water quality 
conditions remains the greatest obstacle to seagrass 

restoration worldwide. 


We know a substantial amount about seagrasses in 
many parts of the world, but there remain considerable 
gaps in our knowledge. As the taxonomies of various 
species are revised, even our understanding of how 
many species of seagrass there are will be subject to 
debate and change. 

The range of individual seagrass species is 
presented in a new series of maps. By combining these 
range maps we are also able to look at biodiversity 
patterns in seagrasses as a whole. The primary 
centers of seagrass biodiversity are identified here as 
insular Southeast Asia, Japan and southwest 
Australia, with additional areas in southern India and 

Photo: F. Gell 




eastern Africa. While there are some important 
parallels between seagrasses and the two other major 
tropical coastal ecosystems of coral reefs and 
mangroves, there are also important divergences, 
notably with the seagrass centers of diversity in Japan 
and in southwestern Australia but also with the 
occurrence of seagrasses in high latitudes as well as 
the tropics. 

It is clear that, despite the relative paucity of 
seagrass species, as a habitat these communities are 
in fact highly diverse. There are many thousands of 
species recorded living in association with seagrass 
communities, although only a small proportion of these 
are strictly confined to seagrass ecosystems. There is 
an urgent need to develop a more comprehensive 
understanding of the full range and diversity of life in 

The work presented here includes a detailed map 
of the known locations of seagrass habitats around the 
world. Once again we are made aware of considerable 
gaps in our knowledge. There is an urgent need for 
clearer documentation of the existence and location of 
seagrass ecosystems in western South America and in 
West Africa, for example. Even within areas of high 
seagrass biodiversity, in many cases little is known 
about the actual distribution of seagrasses. Much of 
our data for the World Seagrass Distribution Map is 
based on individual points of occurrence and not on 
area of coverage. The importance of the high levels of 
primary productivity in seagrasses is well known, and 
these are clearly disproportionate to the total area 
covered by these habitats. It would be invaluable to 
develop an accurate estimate of the total area of 
seagrasses worldwide in order to better analyze the 
role that these may play in global and regional 
fisheries, and in climatic and oceanic carbon cycles. In 
the absence of any better data we have undertaken an 
analysis of seagrass area and suggest a conservative 
estimate of 177000 km’. 

There can be no doubt of the value of seagrasses, 
although such values are often overlooked. For fish, 
many species are not obligatory users of seagrass 
ecosystems, but appear to benefit from their presence. 
Many others use seagrass ecosystems for a short (but 
often critical) part of their life histories, and seagrasses 
are rarely considered in assessing these fisheries. 
Economic evaluations are often constrained by 
analytical procedures and many fail to calculate the 
total economic value of an ecosystem. The critical role 
of seagrasses in stabilizing sediments, reducing 
erosion and even cleaning coastal waters is rarely 
accounted for in such analyses. In addition, other 

measures, which include social welfare, health and 
well-being, are difficult to measure. 

The threats to seagrasses have been widely 
considered by other authors and include natural and 
anthropogenic causes. The latter appear to have 
increased dramatically in recent years, and include 
direct physical destruction and a range of indirect 
threats, the most critical being decreases in water 
clarity resulting from nutrient and sediment inputs but 
also including climate change. In many cases, 
seagrass declines have been linked to multiple 
stresses, acting together. In only a few places around 
the world are measures being taken to address these 
threats. In the present work we have assembled an 
assessment of marine protected areas with 
seagrasses worldwide. Some 247 sites are known to 
include seagrass ecosystems. This is a far lower figure 
than for other shallow marine ecosystems, while 
further concern must be expressed about the 
effectiveness of these sites in protecting seagrasses, 
both from direct impacts and from the indirect impacts 
such as pollution and sedimentation which may be 
carried into the seagrass areas from beyond the 
reserve boundaries. 

The chapters which make up the bulk of this 
work provide a more detailed examination of seagrass 
distribution and of the various themes considered here. 
They provide detailed examples of seagrass com- 
munities around the world, and illustrate issues 
relating to distribution, status and management of 
these beautiful and critically important ecosystems. 


This chapter would not have been possible without the help and input 
from all the participants at the Global Seagrass Workshop which was held 
at the Estuarine Research Federation meeting in St Petersburg, Florida 
in October 2001. The chapter's authors have also drawn heavily on all the 
chapters written by the regional authors (see Table of Contents]. The 
assistance provided by Sergio Martins and Mary Edwards is gratefully 
acknowledged. Jackson Estuarine Laboratory contribution number 397. 


M. Spalding, UNEP World Conservation Monitoring Centre, 219 
Huntingdon Road, Cambridge, CB3 ODL, UK. Contact address: 17 The 
Green, Ashley, Newmarket, Suffolk, CB8 9EB, UK. Tel: +44 (0)1638 
730760. E-mail: mark{ 

M. Taylor, C. Ravilious, E. Green, UNEP World Conservation Monitoring 
Centre, 219 Huntingdon Road, Cambridge, CB3 ODL, UK. 

F. Short, University of New Hampshire, Jackson Estuarine Laboratory, 85 
Adams Point Road, Durham, NH 03824, USA. 






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utilization of Posidonia australis, Notes compiled by CM Stewart 
and JA Mills. CSIRO Division of Chemical Technology, South 

Walker DJ [1977]. Report of the Seaweed Problem on Taperoo 
Beach. South Australian Coast Protection Board Report. 

van Katwijk MM [2000]. Zostera marina and the Wadden Sea. In: 
Sheppard, C led) Seas at the Millennium: An Environmental 
Evaluation, Vol 3. Elsevier Science, Amsterdam. pp 6-7. 

Patriquin DG [1975]. Migration of blowouts in seagrass beds at 
Barbados and Carriacou West Indies and its ecological and 
geological implications. Aquatic Botany 1: 163-189. 

Talbot MMB, Knoop WT, Bate GC [1990]. The dynamics of estuarine 
macrophytes in relation to flood/siltation cycles. Botanica Marina 
33: 159-164. 

Lee Long W, Thom RM [2001]. Improving seagrass habitat quality. 
In: Short FT, Coles RG {eds} Global Seagrass Research Methods. 
Elsevier Science, Amsterdam. pp 407-424. 

Short FT, Short CA [1984]. The seagrass filter: Purification of 
estuarine and coastal waters. In: Kennedy V [ed] The Estuary as a 
Filter. Academic Press. pp 395-413. 

Ward TJ [1987]. Temporal variation of metals in the seagrass 
(Posidonia australis] and its potential as a sentinel accumulator 
near a lead smelter. Marine Biology 95: 315-321. 

Hoven HM, Gaudette HE, Short FT [1999]. Isotope ratios of 
206Pb/207Pb in eelgrass, Zostera marina, indicate sources of Pb in 
an estuary. Mar Env Res 48: 377-387. 

Klumpp DW, Howard RK, Pollard DA [1989]. Trophodynamics and 
Nutritional ecology of seagrass communities. In: Larkum AWD, 
McComb AJ, Shepherd SA {eds} Biology of Seagrasses - A Treatise 
on the Biology of Seagrasses with Special Reference to the 
Australian Region. Elsevier, New York. pp 394-457. 

Lanyon J, Limpus CJ, Marsh H [1989]. Dugongs and turtles: 
Grazers in the seagrass system. In: Larkum AWD, McComb AJ, 
Shepherd SA [eds] Biology of Seagrasses - A Treatise on the 
Biology of Seagrasses with Special Reference to the Australian 
Region. Elsevier, New York. pp 610-634. 

Gell FR, Whittington MW [2002]. Diversity of fishes in seagrass beds 
in the Quirimba Archipelago, northern Mozambique. Marine and 
Freshwater Research 53: 115-121. 

Gambi MC, Nowell ARM, Jumars PA [1990]. Flume observations on 
flow dynamics in Zostera marina (eelgrass) beds. Marine Ecology 
Progress Series 61: 159-169. 

Koch EW, Verduin JJ [2001]. Measurements of physical parameters 
in seagrass habitat. In: Short FT, Coles RG (eds) Global Seagrass 
Research Methods. Elsevier Science, Amsterdam. pp 325-344. 
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seagrass beds: A review of the influence of plant structure and prey 
characteristics on predator-prey relationships. Estuaries 7: 339- 

Phillips RC, Durako MJ [2000]. Global Status of Seagrasses. In: 
Sheppard C [ed] Seas at the Millennium: An Environmental 
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Balino BM, Fasham MJR, Bowles MC [eds] [2001]. GBP Science, 2: 
Ocean Biogeochemistry and Global Change. International 
Geosphere-Biosphere Programme, Stockholm. 

Short FT, Neckles AH [1999]. The effects of global climate change 
on seagrasses. Aquatic Botany 63: 169-196. 

Heck C [2001]. The economics of seagrass. Viewed online June 
2002 at http://www. 
Community Outreach, Florida Keys National Marine Sanctuary. 
Costanza R, Arge R d’, Groot R de, Farber S, Grasso M, Hannon B, 
Limburg K, Naeem S, O'Neill RV, Paruelo J, Raskin RG, Sutton P, 
Belt M van den [1997]. The value of the world’s ecosystem services 
and natural capital. Nature 387: 253-260. 

Short FT, Wyllie-Echeverria S [2000]. Global seagrass declines and 
effects of climate change. In: Sheppard C (ed) Seas at the 
Millennium: An Environmental Evaluation, Vol. 3. Elsevier Science, 
Amsterdam. pp 10-11. 

Milne LJ, Milne MJ [1951]. The eelgrass catastrophe. Scientific 
American 184: 52-55. 

Rasmussen E [1977]. The wasting disease of eelgrass {Zostera 
marina] and its effects on environmental factors and fauna. In: 
McRoy CP, Helfferich C eds) Seagrass Ecosystems: A Scientific 
Perspective. Marcel Dekker, New York. pp 1-52. 

Short FT, Muehlstein LK, Porter D [1987]. Eelgrass wasting 
disease: Cause and recurrence of a marine epidemic. Biological 
Bulletin 173: 557-562. 

Muehlstein LK, Porter D, Short FT [1991]. Labyrinthula zosterae sp. 
Nov., the causative agent of wasting disease of eelgrass, Zostera 
marina. Mycologia 83(2): 180-191. 

Goldschmid A, Yip M [2001]. Essay about Caulerpa taxifolia. 
Salzburg, 6 May 1999 (revised in April 2001). Viewed online May 
2002 at 
Short FT, Wyllie-Echeverria S [1996]. Natural and human-induced 
disturbance of seagrasses. Environmental Conservation 23: 17-27. 
Burke L, Selig L, Spalding M [2002]. Reefs at Risk in Southeast 
Asia. World Resources Institute, Washington, DC. 

Davis RC, Short FT [1997]. Restoring eelgrass, Zostera marina L., 
habitat using a new transplanting technique: The horizontal 
rhizome method. Aquatic Botany 59: 1-15. 

Coles R, Fortes M [2001]. Protecting seagrasses - approaches and 
methods. In: Short FT, Coles RG {eds) Global Seagrass Research 
Methods. Elsevier Science, Amsterdam. pp 445-463. 

Calumpong H, Fonseca M [2001]. Seagrass transplantation and 
other seagrass restoration methods. In: Short FT, Coles RG [eds) 
Global Seagrass Research Methods. Elsevier Science, Amsterdam. 
pp 425-444. 

Short FT, Davis RC, Kopp BS, Short CA, Burdick DM [2002]. Site 
selection model for optimal restoration of eelgrass, Zostera marina 
L. Marine Ecology Progress Series 227: 253-267. 

Granger SL, Traver MS, Nixon SW [2000]. Propagation of Zostera 
marina L. from seed. Ch 107. In: Sheppard CRC (ed) Seas at the 
Millennium: An Environmental Evaluation. Vol. \II, Global Issues 
and Processes. Elsevier Science, Amsterdam. pp 4-5. 

Les DH, Moody ML, Jacobs SWL, Bayer RJ [2002]. Systematics of 
seagrasses (Zosteraceae] in Australia and New Zealand. J Sys 
Botany 27: 468-484. 

Hall MO, Durako MD, Fourqurean JW, Zieman JC [1999]. Decadal 
scale changes in seagrass distribution and abundance in Florida 
Bay. Estuaries 22(2B): 445-459. 

Campey ML, Waycott M, Kendrick GA [2000]. Re-evaluating species 
boundaries among members of the Posidonia ostenfeldii species 
complex (Posidoniaceae] - morphological and genetic variation. 
Aquatic Botany 66: 41-56. 

Waycott M, Freshwater DW, York RA, Calladine A and Kenworthy WJ 
(2002). Evolutionary trends in the seagrass genus Halophila (Thouars): 
insights from molecular phylogeny. Bulletin of Marine Science. 

1 The seagrasses of 

Scandinavia and the Baltic Sea 


global seagrass resource; however, the first 

reports on the importance of seagrass meadows 
for coastal ecosystems derive from this area, from 
Denmark''“|. This chapter summarizes the distribution 
and importance of eelgrass, Zostera marina, in 
Scandinavian and Baltic coastal waters. Although most 
of the quantitative information is based on research 
carried out in non-tidal areas of Denmark, Sweden and 
Finland, the approach is holistic, and includes 
distribution maps and anecdotal information on 
eelgrass from Iceland, Norway and the coastal areas of 
the Baltic Sea, including Germany, Poland, Lithuania, 
Latvia and Estonia [see Map 1.1). 

Gases supports only a small fraction of the 



In the north Atlantic, eelgrass is found around Iceland, 
where about 30 sites have been identified since the 
1950s". Eelgrass forms isolated populations on 
shallow exposed and sheltered sandy bottoms along 
the entire Norwegian coast” and extends into the White 
Sea. The only Norwegian seagrass paper reports 
eelgrass densities between 50 and 160 shoots/m* and 
canopy heights generally between 15 and 60 cm, 
although in extreme cases the length of an individual 
plant may exceed 180 cm". Areas of low density have 
the highest canopies. The average biomass [April- 
November}-at the two sites studied was 20 and 40 g dry 
weight/m?, respectively (range: 12-60 g dry weight/m’, 
Figure 1.1] The associated fauna is rich (265 taxa, 
including mobile macrofauna and epiphytes] and 
ranges between 5 000 and 10 000 individuals/m’. The 
crustacean species assemblage is dominated by six or 
seven families of amphipods, while the epiphytic 
community is characterized by hydroids, bryozoans and 
crustose and upright algae’. Consequently, these 
shallow, vegetated sites are of great importance for 
young year classes of fish in the Skagerrak area’””. 

C. Bostrom 
S.P. Baden 
D. Krause-Jensen 

The Swedish west coast and Denmark 
On the Swedish west coast, as well as in Danish waters, 
eelgrass is the most widely distributed seagrass, and 
dominates sandy and muddy sediments in coastal 
areas of low to moderate wave exposure. In Denmark, 
very exposed areas facing the North Sea are devoid 
of eelgrass. Along moderately exposed Danish and 
Swedish coasts eelgrass forms extended belts 
interrupted by sandbars, while protected eelgrass 
populations generally form more coherent patches. 
Due to its wide salinity tolerance (5-35 psu)'”, eelgrass 
grows in the inner parts of brackish estuaries and 
sheltered bays and in fully marine waters. In areas of 
low salinity, Ruppia spp. and Zostera noltii can co-occur 
at the inner edges (0.5-1.5 m depth) of eelgrass. 
Eelgrass occurs from shallow (0.5-1 m) water 
down to maximum colonization depths that often match 
the Secchi depth. In the inner parts of estuaries, the 
maximum colonization depth is about 3 m, in outer 
parts 4 m and along open coasts about 5 m'""". In rare 
cases of very clear waters, eelgrass penetrates to 10m 
mean sea level (tidal range +0.1 to 0.4 mJ. Eelgrass 
displays a bell-shaped distribution pattern along the 
depth gradient, with maximum abundance at 
intermediate depths and lower abundances in shallow 
and deep water’ '. The biomass of Danish and 
Swedish eelgrass populations peaks in late summer at 
levels reaching above 250 g dry weight/m*. Maximum 
shoot densities range between 1000 and 2500 
shoots/m?'*'*". Exposure, desiccation and ice scour 
may reduce seagrass abundance in shallow water, 
while reductions in seagrass abundance towards the 
lower depth limit correlate with light attenuation along 
the depth gradient'® *7". 

In southernmost Sweden, eelgrass meadows 
flourish on stony and sandy bottoms at 2-4 m depth, 
and may reach densities and standing crops 
corresponding to 3600 shoots/m* and 470 g dry 
weight/m’, respectively {site 11 in Figure 1.1)". The 

i a 











Figure 1.1 

Average [+1 SE] above-ground biomass values (g dry weight/m’) 
for eelgrass (Zostera marina] along the Baltic Sea coastline 

(>1 500 km) 

Source: Various sources” 

Oresund area between Denmark and Sweden (sites 8- 
10 in Figure 1.1) also supports well-developed eelgrass 
meadows at 1.5-6 m depth'”. In September 2000, four 
eelgrass sites along this 100-km coastline showed the 
following features: coverage: 20-80 percent; density: 
293-1 573 shoots/m’; above-ground biomass: 69-193 g 
dry weight/m’; shoot length: 25-125 cm; and shoot 
width: 0.2-0.5 cm”. 

There are qualitative and quantitative data on the 
leaf fauna (defined as the sessile and motile fauna 
living on the leaves], mobile epifauna [intermediate 
predator invertebrates and fish) and piscivore fish 
(secondary predators) from the Swedish west 
coast'”*"!, Data on infauna are more scarce” *. Due to 
the high organic content of most western Swedish 
seagrass beds (2-24 percent ash-free dry weight}, the 
infauna (40-130 000 individuals/m’) is dominated by 
polychaetes and nematodes. The leaf fauna is 
dominated by tube-building amphipods, mainly 
detritivores and suspension feeders (80-250 000 
individuals/m’*), whereas the abundance of herbivores 
is low. Shrimps and crabs make up 90 percent of the 
mobile epifauna, and fishes constitute only about 10 
percent of the intermediate predator abundance (30- 
160 individuals/m’, with maximum abundances in late 
summer]. The piscivore fishes (eelpout, cod and 
salmon] are few during daytime’. Faunal communities 
of Danish eelgrass beds are similarly rich, but have 
received little attention since the 1960s! and 1970s”, 

Western Baltic Sea and Germany 

The western Baltic Sea, composed of the Kiel and the 
Mecklenburger Bights, is a transition zone between 
marine [North Sea] and brackish (Baltic proper) water 
and shows fluctuations in salinity (generally 10-18 psu 
but occasionally 8-28 psu” *”}. In this region eelgrass 
is found both along exposed sandy shores and in long, 
inner bays ("Forden") and shallow lagoons ("Bodden", 
“Haffs") with reduced water exchange and muddy 
substrate’ *". Along exposed shores, the upper limit 
of distribution is set by wave-induced disturbance. 
Typically, continuous beds are found from 2.5 m depth 
and deeper. Additionally, patchy beds are found 
between the sand reefs and the shore at depths of 1- 
2m. In sandy areas, eelgrass grows down to a depth 
of 8 m, and there is an almost continuous belt of 
eelgrass all along the shoreline, although on gravel- 
and stone-dominated substrates plants are rare. 
Extended populations are found in Orth Bay, in Kiel 
Fjord [(Falkenstein) between Travemiinde and 
Klutzhoved, in the Wismar Bay and north of Zingst 
Peninsula’. Zostera noltii has been reported from 
Schleimunde, Heiligenhafen, Wismar Bay and 
Greifswald Lagoon". 

In the Kiel area (Belt Sea) the eelgrass growing 
period is approximately 210 days, and growth is initiated 
in June, peaks in August-September and stops in 
March. Shoot lengths range between 20 and 140 cm'*:*!. 
In Kiel Fjord (Friedrichsort and Moeltenort), eelgrass 
density is 600-1 600 shoots/m?'”. The biomass range in 
Kiel Bight is 450-600 and 200-800 g dry weight/m* on 
mud and sand, respectively, and the daily production is 
1.5-2.2 g carbon/m’'*". In the 1970s, the mean annual 
eelgrass standing stock for two sites in Schleswig- 
Holstein (Kiel Bight) was 42.5 metric tons/ha””. 

A typical feature of shallow (depths of 1-3 m) 
eelgrass beds is their co-occurrence with blue mussels 
(Mytilus edulis), which represents a facultative 
mutualism™”. Isopods (/dotea spp.) and snails 
(Hydrobia spp., Littorina spp.) are abundant grazers, 
and remove eelgrass biomass and_ epiphytes, 
respectively, highlighting the importance of biological 
interactions, which may locally override the negative 
symptoms of eutrophication’. In shallow lagoons 
(e.g. Schlei Estuary], eelgrass is also consumed by 
birds, especially mute swans (Cygnus olor). 

The Swedish east coast 

Eelgrass penetrates into the brackish (0-12 psu) Baltic 
Sea, and is common in most coastal areas. The northern 
and eastern distribution limits of eelgrass correlate with 
the 5 psu halocline. The usual depth of eelgrass in the 
Baltic Sea is 2-4 m [range 1-10 m). Zostera noltii extends 
to southern Sweden, and to Lithuania in the eastern 
Baltic’. At present, the northern limit of Zostera noltiiin 




« ,Gullmarsfjord 
s e/ 
Kristiansand he Skaft6 
; E ‘ 
Skagerrak —*& stenungssund 

Limfjorden. Vastervike? 
—— - @ Vendelséfjord P 
am Katlegat 


Hallands Vadero ¢ ! 

¢ % 
Landskrona ] 
/ =- e.: 


“hg . 


—“. “ Limhamn 
3 4 t Fredshog 
=i ® Sandhammaren 
Ss %& < —Oresund 
2 be: Bomholm 
« Kiel Bight Zinyst Peninsula 
© Oh Rigen 
Heiligenhaten! Bag Greifswald 
Ye freer f Lagoon 
Mecklenburger Bight’ __GERMANY 
Map 1.1 

the Baltic Sea is unknown. Due to lack of tides, all 
seagrass beds in the Baltic Sea are permanently 
submerged, and often mixed with limnic angiosperms 
(e.g. Potamogeton spp. and Myriphyllum spp.). 

On the brackish (6-8 psu) east coast of Sweden, the 
most extensive eelgrass meadows are probably found in 
the sandy Kalmarsund-Oland. Along the southeastern 
coast of Sweden (Sandhammaren to Vastervik], eelgrass 
is common on sandy bottoms with good water exchange. 
The demographic information from this area is based on 
anecdotal evidence, diving observations made during 
coastal monitoring (University of Kalmar], and 


Curonian Spit 


Scandinavia and the Baltic Sea 



Sea eco 


“<* Gulf of 

i = 
of tvarminne F inland 

Po Hanko Peninsula 

© “Mrchipelago of 


a SEA 

a * Gulf of 

. Riv 
Gotland ee 


Puck Lagoon 

© Gdansk 
O 50 100 150 200 250 Kilometers 

unpublished data by S. Tobiasson. Dense shallow stands 
have short (20 cm], narrow (2-3 mm] leaves and usually 
grow in mixed stands with Potamogeton pectinatus, 
Ruppia maritima, Zannichellia palustris and 
bladderwrack Fucus vesiculosus, while the deepest 
stands are sparse, monospecific and have longer (>80 
cm] and broader (5 mm) leaves. 

The coverage pattern is usually patchy (patch area 
10-50 m? with a mean coverage of 50-75 percent, range 
5-100 percent). At the main distribution depth, the mean 
shoot density is 500-600 shoots/m’, but ranges between 
100 and 1040 shoots/m’, depending on depth. The 

\) \ y 



Photos: J. Lindholm 


Figure 1.2 
Aerial photographs of two typical exposed eelgrass (Zostera 

marina) sites at the Hanko Peninsula, southwest Finland, northern 
Baltic Sea (adjacent to site 16 in Figure 1.1] 

a. Kolaviken (59°49'N, 22°59'E): the high-energy regime at this site 
is reflected in a complex, patchy bed structure. 

b. Ryssholm (59°60'N, 23°05'E): the continuous eelgrass bed is 
interrupted by sandbars, while circular to highly irregular, 
elongated patches are found at the outer edge of the bed. 

Notes: The areas covered by eelgrass in [a] and (b] are 23 and 6 hectares, 
respectively. The depth range covered by eelgrass is approximately 2-6 m. 

above-ground biomass may exceed 100 g dry weight/m’ 
(site 13 in Figure 1.1). The steep, exposed coastal areas 
of southern Sweden (Skane] and the east coast of the 
Oland Island lack eelgrass". The semi-exposed sandy 
shores of Gotland Island support extensive eelgrass 
meadows. The northern limit of distribution is in the 
northern Archipelago of Stockholm”! Few studies of the 
associated fauna have been carried out’ *”, but these 
meadows support more than 20 infaunal species and a 
rich leaf fauna with over 30 species!” 

Finland and Aland Islands 

In Finland, eelgrass grows exclusively on exposed or 
moderately exposed bottoms with sandy sediments. 
The spatial patterns of eelgrass beds in shallow water 

TR ae 

are mainly controlled by physical factors (Figure 1.2). In 
the Archipelago Sea, eelgrass beds are found towards 
the leeside of islands, while more sheltered, inner bays 
on the mainland do not support eelgrass beds. 
Eelgrass sites in Finland vary in terms of patch size [(1- 
75 m‘}, shoot density (50-500 shoots/m’), shoot length 
(20-100 cm), biomass (10-32.1 g ash-free dry 
weight/m’“”' and sediment properties (organic content 
0.5-1.5 percent, grain size 0.125-0.5 mm). The low 
shoot densities result in low areal production rates 
(138-523 mg dry weight/ m’*/day'"']. The associated 
fauna of Finnish seagrass beds is well described”. A 
rich sedimentary fauna (25 000-50 000 individuals/m’, 
50 species“ and a distinct leaf fauna!) 
contributes significantly to coastal biodiversity in 
Finland. Northern Baltic seagrass communities lack 
crabs and echinoderms, and the nursery role for 
economically important fish species is limited, but 
seagrass beds serve as feeding grounds for fish. 


The direct use and manufacture of eelgrass-based 
materials has been local and intermittent. In Denmark 
and other countries dried eelgrass leaves have been 
used as fuel, packing and upholstery material, insulation 
and roof material, feeding and bedding for domestic 
livestock, fertilizer and as a resource to obtain salt": “*“"!. 
In Sweden, dried eelgrass leaves have mainly been used 
for insulation of houses. Historically, the abundant 
eelgrass resources of the sheltered lagoons in the 
western Baltic Sea [Germany] have been utilized for 
upholstery and insulation. The last eelgrass collector at 
Maasholm, Germany, retired in the 1960s. In the 
southeastern Baltic Sea, human communities on the 
Curonian Spit (Lithuania) used eelgrass as upholstery 
material before the Second World War, indicating 
abundant eelgrass meadows in the area before the 
1940s". The current appreciation of seagrasses 
primarily concerns the services that seagrasses provide 
to the overall functioning of coastal ecosystems in terms 
of enhancing biodiversity, providing nursery and foraging 
areas for commercially important species, improving 
water quality by reducing particle loads and absorbing 
dissolved nutrients, stabilizing sediments and 
influencing global carbon and nutrient cycling'”. 



Along the southeastern coast of Norway (between the 
Norwegian-Swedish border and Kristiansand], almost 
100 sites have been monitored since the 1930s in 
connection with beach seine surveys each autumn 
{September-October) by the Institute of Marine 
Research”. The presence of vegetation has been 
estimated by aquascope, and seagrass cover has been 

divided into the following categories: 1 = no vegetation, 2 
= few plants, 3 = some plants, 4 = many plants, 5 = 
bottom totally covered. Unfortunately, only a small 
fraction of this dataset has been compiled and most is 
unpublished. The general impression, however, is that 
the coverage of eelgrass increased during the 1930s, and 
since then it has varied irregularly (Figure 1.3 a, b). Some 
areas showed signs of reduction in the late 1960s, and 
apparently there was a reduction probably indirectly 
related to the great bloom of Chrysochromulina in 1988. 
Now the coverage seems generally to be good’. 

The western and eastern coasts of Sweden 
During the 1980s inventories of the shallow coastal 
areas including eelgrass were carried out along the 
Swedish west coast as a basis for coastal zone 
management. In 2000, a revisit and inventory of 20 km’ of 
eelgrass meadows in five coastal regions along 200 km 
of the Skagerrak coast was carried out using the same 
methods (aquascope] as during the 1980s, but mapping 
accuracy was improved by using the global positioning 
system (GPS]. This study showed that areal cover had 
decreased 58 percent (with regional variations) in 10-15 
years. In the 1980s, eelgrass covered about 20 km’ of 
bottom along this 200-km section of the west coast, 
while only about 8.4 km’ was present in 2000". Since 
1994, one eelgrass site in southwest Sweden near 
Trelleborg (site 11 in Figure 1.1) has been included in the 
local coastal monitoring program. Shoot density and 
biomass of eelgrass at this site has increased 
significantly since 1994 (linear regression for biomass: 
p<0.001, r = 0.81), and this positive trend seems to be 
true for many of the eelgrass monitoring sites in the 
Oresund region (sites 8-11 in Figure 1.1'") probably due 
to greater exposure and/or invertebrate grazing’"'. No 
estimates of the total area covered by eelgrass along the 
whole Swedish west coast (>400 km] exist. An estimation 
of the total eelgrass coverage along the southeastern 
Swedish coast [including the Oland Island) yields 
minimum and maximum numbers between 60 and 130 
km’, respectively”. Between this region and the 
northern distribution limit in the Stockholm Archipelago 
eelgrass is still common, but far less abundant due to 
lack of suitable substrate®”. 


In Denmark, records of eelgrass distribution date back to 
around 1900, and provide a unique opportunity to 
describe long-term changes. In 1900, eelgrass was 
widely distributed in Danish coastal waters, and covered 
approximately 6 726 km’ or one seventh of all Danish 
marine waters (Figure 1.4'**]. The standing crop ranged 
between 270 and 960 g dry weight/m’, in sparse and 
dense stands, respectively, and total annual eelgrass 
production was estimated at 8 million metric tons dry 

Scandinavia and the Baltic Sea 

Figure 1.3 
Norwegian eelgrass coverage 


80 90 2000 

. Long-term trends in the presence of eelgrass (Zostera marina) 
at shallow, soft-bottom sites assessed by aquascope in 
southeastern Norway (Kristiansand to the Norwegian-Swedish 
border] during the period 1933-2000. 


Monotypic Zostera marina 

Mixed Zostera marina 


b. Coverage at sites where eelgrass occurs in single stands (green 
line) and mixed with benthic algae (black line). 

Notes: 1 = no coverage, 5 = bottom totally covered. Number of sites 
sampled each year (38-134, mean 93] vary due to variation in water 
turbidity. No data obtained during 1940-44. 

Source: Norwegian Institute of Marine Research 

weight”. In the 1930s, wasting disease led to substantial 
declines in eelgrass populations, especially in northwest 
Denmark where salinity is highest (Figure 1.4°]. In 1941, 
eelgrass covered only 7 percent of the formerly 
vegetated areas, and occurred only in the southern, most 
brackish waters and in the low-saline inner parts of 
Danish estuaries (Figure 1.4% *'). No national 
monitoring took place between 1941 and 1990, but 
analyses of aerial photos during the period from 1945 to 
the 1990s show an initial lag after the wasting disease 
followed by marked recolonization in the 1960s" °”) 
Today eelgrass again occurs along most Danish 
coasts but has not reached the former areal 
extension’ *”. Based on comparisons of eelgrass area 
distribution in two large regions, Oresund and 
Limfjorden, in 1900 and in the 1990s, we estimate that 
the present distribution area of eelgrass in Danish 


Figure 1.4 

Map of eelgrass area distribution in Danish coastal waters in 1901, 1933, 1941 and 1994 

North Sea 


Baltic Sea 

North Sea y 1933 


Baltic Sea 


\ y 
§Za\ Germany J 
237° eat 

Baltic Sea 

North Sea 7) 1994 

q Sweden 


Notes: Dark green areas indicate healthy eelgrass while black areas (on the 1933 map] indicate where eelgrass was affected by the wasting disease but 

still present in 1933. The arrow shows the location of Limfjorden. 

Source: Various sources: 1901 [redrawn”), 1933 (redrawn), 1941 (redrawn'®*!) and 1994 (coarse map based on visual examination of aerial photos and 
data from the national Danish monitoring program, produced by Jens Sund Laursen) 

coastal waters constitutes approximately 20-25 percent 
of that in 1900 (Figure 1.4). The area distribution of 
eelgrass in Limfjorden was thus estimated at 345 km’? 
in 1900"! and at only 84 km? in 1994 (based on aerial 
photography data from the Limfjord counties]. In 
Oresund, eelgrass covered about 705 km? in 1900"! and 
only about 146 km? in 1996-2000". Differences in 
methodology influence these comparisons since the 
distribution maps of eelgrass from the beginning of the 
last century were based on extrapolation between sites 

visited in field surveys, while maps from the 1990s were 
based on image analysis of aerial photography. This 
large areal reduction is partly attributed to the loss of 
deep eelgrass populations as a consequence of 
impoverished light conditions due to eutrophication. In 
1900, maximum colonization depths averaged 5-6 m in 
estuaries and 7-8 m in open waters (Figures 1.5 and 
1.6]. In the 1990s, colonization depths were reduced by 
about 50 percent to 2-3 m in estuaries and 4-5 m in 
open waters. 

Colonization depth 
in estuaries 

Colonization depth 
along open coasts 
40 1900 



fej eaye (0 
Bo 0 2) 0) 2 
Colonization depth (m) 

Figure 1.5 
Maximum colonization depth of eelgrass patches in Danish 
estuaries and along open coasts in 1900 and 1996-97 

Source: Based on data from 12 sites in estuaries and 18 sites along open 
coasts investigated by Ostenfeld'“’ in 1900 and by the national Danish 
monitoring program in 1996-97 

Germany, Poland and Lithuania 

In Germany (Kiel Bight), eelgrass competes with 
increasing amounts of filamentous algae, and in some 
areas the depth distribution of eelgrass decreased from 
6 m in the 1960s to less than 2 m at the end of the 
1980s'"'. In the Greifswald Lagoon [island of Rigen), 
the distribution of eelgrass has remained fairly stable, 
despite the almost total disappearance of red algal 
belts during the period 1930 to 1988". Nevertheless, 
eelgrass is by far the most abundant macrophyte on 
sandy to muddy shores in this area’”’. 

In Poland (Gulf of Gdansk, Puck Lagoon], abundant 
eelgrass meadows grew down to a depth of 10 m in the 
1950s, but were almost totally replaced by filamentous 
brown algae and Zannichellia palustris during the period 
1957-87"! (Figure 1.7). The change from dense sea- 
grass beds to algal-dominated assemblages has caused 
a shift in the commercially important fish communities. 
Hence, eel (Anguilla anguilla) and pike (Esox lucius) have 
decreased in abundance and have been partly replaced 
by roach (Rutilus rutilus)'**”. In addition, eelgrass 
suffers from heavy metal contamination’. 
Transplantation of eelgrass has been tested in the Puck 
Lagoon’. Recently natural recolonization has taken 
place in some areas of this lagoon”. 

Along Lithuanian coasts in the southeastern 
Baltic Sea, eelgrass had virtually disappeared before 
any scientific evaluation was made. Eelgrass most 
likely occurred along the 90-km-long sea side of the 
Curonian Spit, covering thousands of hectares”. In 

Scandinavia and the Baltic Sea 

»1900 @ 1992 


Secchi depth (m} 

Figure 1.6 
Secchi depths and maximum colonization depths of eelgrass 
patches in Danish estuaries and open coasts in 1900 and 1992 

Source: Measured by Ostenfeld'“’ in 1900 and by the national Danish 
monitoring program in 1992 

1998, filamentous green algae (Cladophora glomerata) 
dominated along the coast, and eelgrass was 
considered rare and endangered; no eelgrass was 
found during underwater surveys during 1993-97°". 

Figure 1.7 
Long-term changes in the distribution of eelgrass (Zostera marina) 
in the southeastern Baltic Sea (Puck Lagoon, Poland) 

Notes: Scale bar in lower right corner corresponds to approximately 
5 km. Green areas indicate eelgrass cover. 

Source: Modified after Kruk-Dowgiallo®” 




One northern site (Palanga) supported eelgrass, 
indicating that eelgrass was probably present formerly 
along the whole Lithuanian coast’’ *!. The seagrass 
literature from Latvia and Estonia is scarce, but 
eelgrass has been reported to occur sparsely among 
algal-dominated assemblages in the Gulf of Riga’””. 


The only long-term analysis of an eelgrass site in 
southwest Finland recorded no change in density and 
standing stock between 1968 and 1993’. In 1993, 
eelgrass biomass was about 85 g dry weight/m’ and 
corresponded well with the yearly means for 1968-70 in 
terms of ash-free dry weight (20 g/m’). By contrast, the 
associated eelgrass fauna showed marked signs of 
eutrophication. Total abundance of infauna had 
increased almost fivefold, and the total animal biomass 
had more than doubled over 25 years. The number of 
taxa showed minor changes over time. These faunal 
changes indicate increased food availability, due to 
eutrophication. Unfortunately, no long-term data from 
other Finnish eelgrass sites exist to verify this result. 
Genetic analysis of Finnish eelgrass meadows suggests 
an age of these plant ecosystems between 800 and 1 600 
years'” ”!, indicating that eelgrass colonization must 
have taken place at present salinities. Those eelgrass 
populations near their limit of distribution in terms of 
salinity were not affected by the wasting disease in the 
1930s” and have also persisted through severe 
anthropogenic stress and long-term physical stress in 
terms of landlift, wind disturbance, sedimentation and 
fluctuations in temperature and ice cover. Based on very 
crude areal estimates, and extrapolations from the 
number of known eelgrass sites verified by diving (totally 
about 50 sites), our guess is that the total coverage of 
eelgrass in Finland is probably less than 10 km’. 


Kattegat and Skagerrak 

Since the lower depth limit of eelgrass is determined by 
water transparency, eutrophication is a main threat to 
especially deep eelgrass populations. Maximum Secchi 
depths and colonization depths approached 12m in 
open Danish waters in 1900 but rarely exceeded 6m 
in the 1990s (Figure 1.6). The maximum colonization 
depth is also correlated to the concentration of water 
column nitrogen, which is the main determinant of 
phytoplankton biomass in Danish coastal waters”. 
Eutrophication-gained filamentous algae (mainly 
ephemeral] may shade seagrasses, hamper water 
exchange and cause a decline in associated faunal 
communities, e.g. shrimps and crabs!" 1?” In 
shallow stagnant waters with limited oxygen pools, as 
well as in deeper stratified waters, the oxygen- 
consuming decomposition of ephemeral algae and 

detritus may lead to anoxia. High water temperature 
also stimulates microbial decomposition rates and 
thereby further increases the risk of anoxia. Oxygen 
deficiency in the meristematic region of eelgrass is a 
likely key factor explaining events of mass mortality in 
eelgrass beds", possibly in combination with sulfide 
exposure”. Shallow eelgrass populations often show 
large and rapid fluctuations, suggesting that stochastic 
interactions between water temperature, light, 
nutrients and physical disturbance like strong wave 
action and ice scouring play important regulating roles, 
and that recolonization may also happen relatively fast 
in deeper water if conditions improve’ *”. 

Other threats include siltation and mechanical 
damage. For example, the construction in 1995-2000 of 
the Oresund bridge between Denmark and Sweden, 
almost 8 km long and one of the most massive marine 
constructions in Scandinavia, was likely to affect the 
large eelgrass populations in Oresund. However, strict 
regulations on dredged quantities and spillage during 
the construction works prevented detectable negative 
impacts on eelgrass” 77! 

In some Danish estuaries where eelgrass and 
blue mussel occur in mixed populations, mussel 
fishery may constitute a threat to eelgrass 
populations”. In Sweden the increasing leisure boat 
harbors with uncontrolled anchoring, dredging and 
water currents from propellers are the main physical 
threats to seagrass meadows. 

The Baltic Sea 

As in Denmark and Sweden, the drifting and sessile 
forms of fast-growing, filamentous algae constitute a 
serious threat to seagrasses in other areas of the 
Baltic®’”"*", which will probably have negative effects on 
the whole eelgrass community”. During the past ten 
years, increasing amounts of ephemeral, filamentous 
algal mats have been observed at shallow localities in 
the northern Baltic Sea“, with profound negative 
effects on the benthic communities". In 1968-71 
filamentous algal mats were already common at 
eelgrass sites, but their biomass was less than 5 g ash- 
free dry weight/m?“". Today, the biomass of drifting 
algae in Finland commonly exceeds 1000 g dry 
weight/m?'”'* and subsequent periodic anoxia is also 
common in shallow areas. It is clear that these algae are 
a major threat to the Baltic Sea seagrass ecosystems. In 
the heavy traffic coastal areas of the Baltic Sea, oil spill 
accidents could be detrimental to seagrass vegetation. 
Other threats include sand suction and construction. 


Several political initiatives affect Scandinavian seagrass 
populations. In 1987, the Danish Government passed an 
Action Plan on the Aquatic Environment including 

measures on wastewater treatment, the storage of 
animal manure and reductions of agricultural nitrogen 
and phosphorus. The aim was to reduce annual total 
nitrogen discharge by 50 percent, and that of phosphorus 
by 80 percent, within five years. A second action plan 
containing further measures was passed in 1998 to 
ensure that the planned reductions of nitrogen and 
phosphorus discharges will be in effect before 2003. In 
addition there are several directives concerning point 
sources and _ protection of groundwater. An 
announcement on mussel fishery in Denmark prohibits 
fishery at water depths shallower than 3 m in order to 
protect eelgrass beds. A nationwide Danish monitoring 
program was established in 1988 to demonstrate the 
effects of the Action Plan (for latest adjustments, see 
Environmental Protection Agency). Large construction 
works typically have associated monitoring programs, as 
was the case for the fixed link across Oresund. 

As in Denmark, a series of action plans aiming to 
reduce nutrient discharge have been agreed in Sweden 
since the late 1980s, but not fulfilled. The latest action 
plan against coastal nutrient pollution is part of 
Swedish national environmental goals {Governmental 
Proposition 2000), and specifically says that total 
nitrogen discharge with anthropogenic origin from land 
should be reduced by 30 percent from 1995 not later 
than 2010, whereas phosphorous should decrease 
continuously from 1995 to 2010 with no specific aim. 
However, not only nutrient pollution but also 
overfishing might be part of the decreasing extension of 
seagrass through a possible, but still unverified, top- 
down control mechanism”. In the Baltic, as well as in 
the Kattegat and Skagerrak, most fish stocks are 
overfished to levels below biological safe limits. This is 
a much-debated topic, but has so far not been the 
subject of serious action plans. 

Finland is not committed to monitor seagrass 
meadows. However, Finland follows political agree- 
ments, which are carried out by national (e.g. Water 
Protection Targets for 2005, Renewed Nature 
Conservation Act [1996], Renewed Water Act and EIA 
(Environment Impact Assessment) procedures) and 
international (Habitat Directive and Natura 2000) 
environmental programs. Thus, seagrasses in Finland 
are only indirectly protected through limitations on 
nutrient discharges. A new governmental program 
initiated in June 2001 aims at reducing nutrient 
discharges to the Baltic Sea and protecting and 
monitoring marine coastal biodiversity. 

At the international level, seagrasses are listed in 
the Rio Declaration (1992/93:13] as diverse habitats in 
need of protection and monitoring (Chapter 17 part D 
17.86 d). Further, the European Water Framework 
Directive, the Habitat Directive, the Helsinki Convention 
(HELCOM}, the Oslo-Paris Convention (OSPAR) and the 

Scandinavia and the Baltic Sea 

Convention on Biodiversity also place demands for 
monitoring seagrasses in Scandinavia“. More details 
on political initiatives on nutrient reductions and 
monitoring are summarized in Laane et al." (Chapter 
6.2). On the initiative of the Helsinki Commission, a Red 
List of marine biotopes in the Baltic Sea” serves as an 
instrument in conservation, management and policy- 
making. In the Red List “sublittoral sandy bottoms 
dominated by macrophytes” and “sand banks of the 
sublittoral photic zone with or without macrophyte 
vegetation” are classified as “heavily endangered” and 
“endangered”, respectively’. Accordingly, during the 
implementation of the European Union Water Frame- 
work Directive, eelgrass should be included as an indi- 
cator species. In future years, the coverage, depth 
range and biodiversity of eelgrass beds may potentially 
be used for ecological classification of Baltic coastal 
waters. Guidelines for monitoring eelgrass and other 
key macrophytes are included in the HELCOM 
COMBINE program”. 

However, classification of Baltic Sea seagrass 
meadows as threatened is only a first step obligating 
regular quantitative estimates of the distribution 
patterns, dynamics and diversity of seagrass meadows. 
Consequently, these parameters should be obtained 
and evaluated within standardized, national monitoring 
programs. Presently, only a fraction of the Baltic Sea 
seagrass resources undergo regular monitoring. In 
future, such measures are crucial in order to 
understand and sustain these important ecosystems. 


The authors would like to thank the following persons for data, comments 
or logistical support during the preparation of the manuscript: Penina 
Blankett, Hartvig Christie, Jan Ekebom, Stein Fredriksen, Jakob 
Gjoseter, Frida Hellblom, Agnar Ingolfsson, Hans Kautsky, Jonne Kotta, 
Hordur Kristinsson, Jouni Leinikki, Mikael von Numers, Serge} Olenin, 
Panu Oulasvirta, Lars-Eric Persson, Eeva-Liisa Poutanen, Thorsten 
Reusch, Aadne Sollie, Stefan Tobiasson and Jan Marcin Weslawski. 
Susanne P. Baden gained financial support from WWF (World Wildlife 
Fund) and the County of Vastra Gotaland, and Dorte Krause-Jensen from 
the European Union (#EVK3-CT-2001-00065 "CHARM" and EVK3-CT- 
2000-00044 "M&MS"}. 


Christoffer Bostrém, Abo Akademi University, Department of Biology, 
Environmental and Marine Biology, Akademigatan 1, FIN-20500 Abo, 
Finland. Tel: +358 (0)2 2154052, 4631045. Fax: +358 (0)2 2153428. E-mail: 

Susanne P. Baden, Goteborg University, Department of Marine Ecology, 
Kristineberg Marine Research Station, S-45034 Fiskebackskil, Sweden. 

Dorte Krause-Jensen, National Environmental Research Institute, 
Department of Marine Ecology, Vejlsovej 25, 8600 Silkeborg, Denmark. 

W \ JY 
ra a 








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Pachel K, Raike A, Shekhovtsov A, Svendsen L, Valatka S [2002]. 
Evaluation of the Implementation of the 1988 Ministerial Declaration 
regarding Nutrient Load Reductions in the Baltic Sea Catchment Area. 
Finnish Environment Institute, Helsinki. 

Back, S [1999]. Guidelines for Monitoring of Phytobenthic Plant and 
Animal Communities in the Baltic Sea. Annex for HELCOM COMBINE 
programme. 12 pp. 

Institute of Marine Research, Flodevigen Marine Research Station. 
Unpublished data. 




2 The seagrasses of 


estern Europe is considered here as the coasts 
W the North Sea, the Channel and Irish Sea as 
well as the Atlantic coasts of the British Isles, 

France, Spain and Portugal. Two seagrass species are 
found in coastal and estuarine areas: Zostera marina 
and Zostera noltii. A third species, Cymodocea nodosa, 
occurs less abundantly in the southern part of the area 
(Portugal). The widgeon grasses, Ruppia maritima and 
Ruppia cirrhosa, sometimes considered to be 
seagrasses, occur in brackish water sites', such as 
low-salinity ponds and mesohaline to polyhaline 
coastal lagoons; occurrence under marine conditions is 
very rare in western Europe and generally ephemeral. 
The seagrasses are found on soft sediments to a 
maximum depth of about 10 m. They occupy a large 
variety of marine and estuarine habitats. They often 
grow in dense beds and extensive meadows creating a 
productive and diverse habitat used as shelter, nursery, 
spawning or food area by a large variety of animal 
species. Among these, several are of commercial 
interest or cultural value. Therefore, seagrass beds are 
recognized as an important reservoir of coastal 
biodiversity; they shelter in the same _ habitat 
endofaunal and epifaunal species in the sediment, and 
creeping and walking species on the leaves, as well as 
swimming species” ”. Seagrasses are consequently of 
considerable economic and conservation importance. 
The dense root network of the seagrasses is able to 
stabilize the underlying sediment and to increase the 
sedimentation fluxes by reducing the hydrodynamic 
forces. Their essential ecological role in terms of 
primary production at the scale of the coastal 
ecosystem is mainly recognized in the areas where 
hard bottom surfaces with macroalgae cover are 
scarce. The importance of the beds was higher at the 
beginning of the 20th century, before the “wasting 
disease” struck. The proliferation of the pathogenic 
slime mold (Labyrinthula zosterae) in the leaves of 
Zostera marina, considered to be the consequence of 

C. Hily 
M.M. van Katwijk 
C. den Hartog 

weakening of the plants under continuous unfavorable 
environmental conditions, resulted in the 1930s in the 
loss of almost 90 percent of the Zostera marina 
populations of western Europe” *. After this period, 
many beds progressively recovered but the area 
covered remained low in most areas compared with 
previous distribution. Zostera marina lives mainly in the 
infralittoral (or sublittoral]) zone but can develop 
occasionally in the lower and middle part of the 
mediolittoral (or eulittoral) zone. There the species 
develops a morphological variety with narrow and short 
leaves previously considered as a separate species, 
named Zostera angustifolia, and which in many areas 
behaves as an annual. It is noteworthy that in the 
United Kingdom a specific distinction between Zostera 
angustifolia and Zostera marina is still made“. Zostera 
nolti lives higher on the shore and occurs in the middle 
and upper parts of the mediolittoral belt. The species 
can also live under permanent subtidal conditions in 
small brackish streams and coastal lagoons with 
euhaline conditions. 

In the United Kingdom, Zostera marina is the 
more common species; it is widely, but patchily, 
distributed around the coasts of England, Scotland and 
Wales; the main concentrations occur along the west 
coast of Scotland including the Hebrides and in 
southwest England including Devon and Cornwall, as 
well as the Scilly Isles and Channel Islands. The 
intertidal form of Zostera marina is also widely 
distributed, but less abundant; sites with major 
concentrations occur in the Exe Estuary, in Hampshire, 
the Thames Estuary, and the Moray and Cromarty 
Firths in Scotland. Zostera noltii has a predominantly 
eastern distribution in the United Kingdom, more or 
less coinciding with the distribution of the intertidal 
Zostera marina form”. 

In Ireland, Whelan carried out an extensive sur- 
vey of Zostera spp.; Zostera marina is frequently found 
along the coasts under subtidal conditions (Ventry Bay, 

Regional map: Europe 

wy 000L 008 009 00% 002 0 

| i eae 



Vas ‘ 


eO1L TV 


a te) 





oto: F.T. Short 


Fish sheltering in a cluster of sea urchins in an Enhalus acoroides bed, 

Komodo National Park, Indonesia 

E.P. Green 


e [ares ‘ 
ic invertebrates in a bed of Tha Clownfish and anemone in Enhalus acoroides and Thalassia 
hemprichii meadow in Kavieng, Papua New Guinea 

\ 0 100 200 300 Kilometers 
= aa 


Cromarty Firth 

. . 
sae, Moray Firth 

Ringkobing Fjord 

Galway » . eS ina) 
; Firth Frisian Is. 

Strangford * 

@IRELAND Tire : 

. a . 

a7 Ueyn Peninsula aoe 
‘ “ as Samau Thames g.Grevelingen 
Ventry Bay we Estuary . 
we > Solent BELGIUM 50° 
Isle of Wight 

Exe Estuary 
- s 
Scilly Isles, Se irs 

Plymouth Sound 
Ile de Batz—_ Channel Is. 
Moléne oes 
Bay of Brest— 

~Cotentin Peninsula FRANCE 

\ *S Mont St. Michel Bay 
Brehat Archipelago 

Glénan Isles He Gulf of Morbihan 

Map 2.1 
Western Europe (north) 

Galway sites, West Cork sites). Wasting disease 
symptoms were observed in this country in the 1930s”. 

The sandy, surf-exposed North Sea coasts of 
Denmark, Germany, the Netherlands, Belgium and 
France are devoid of seagrass. Seagrasses are 
restricted to the Wadden Sea area, which is protected 
from the full hydrodynamic forces of the ocean by the 
Frisian Islands. Along the Danish west coast, Zostera 
marina occurs in the enclosed Ringkobing Fjord. In the 
southern part of the Netherlands some intertidal popu- 
lations of the two Zostera species occur in the 
estuarine branches of the mouths of the rivers Rhine 
and Meuse. Some of these branches were diked in the 
second part of the 20th century, but still contain some 
submerged beds of Zostera marina (Lake Grevelingen, 
Lake Veere). 

In France, the two Zostera seagrass species are 
widely distributed. The brackish water species Ruppia 
maritima and Ruppia cirrhosa are uncommon and 
mostly encountered in brackish ponds along the 
Channel coast, and the Guérande north of the Loire 
Estuary; their distribution is insufficiently known. Many 
small Zostera marina beds occur along the Channel 
coasts from the west of Normandy to the west of 
Brittany, mainly on the sandy bottom under both 
intertidal and subtidal marine conditions'”. From the 
west of Brittany to the south of the Bay of Biscay, the 
sites are either subtidal around islands (Moléne and 
Glénan Archipelagos) or in very sheltered bays [Bay of 
Brest, Gulf of Morbihan, Arcachon Basin) in which they 
can occupy large areas. 

Western Europe 

Bay of Brest 

Glénan Isles~* 

Gulf of Morbihan 

Loire Estuary 

Marennes-Oléron Basin 

Bay of Biscay 

{reachon Basin 



Ria Formosa 

Alfacs Bay 




Map 2.2 
Western Europe (south] 

In Spain and Portugal, seagrass beds are 
localized in drowned river mouths (rias] and protected 
bays (e.g. Vigo Bay), with a zoned occurrence of 
the two species of Zostera. Zostera noltii occurs on 
the large muddy mediolittoral flats and Zostera 
marina (accompanied sometimes by Cymodocea 
nodosa (e.g. Ria Formosa)) in the upper part of the 
infralittoral. Many of these beds are concentrated in 
the numerous Galician rias in northwestern Spain'”’. 
In Europe, Zostera marina reaches the southern limit 
of its Atlantic distribution in southern Spain near 



Zostera marina occurs under a large range of 

environmental conditions which can be identified as the 

following three main biotopes: 

) Sheltered habitats in enclosed and semi- 
enclosed bays, estuaries and rias, with turbid 
low-salinity waters and muddy sediments. 
Eelgrass beds are limited to a narrow depth range 
{<2 m) and because of the high turbidity do not 
extend much below mean sea level. These beds 
often appear as long narrow [<30 m wide} ribbons 
along the small subtidal channels which groove 
the muddy intertidal flats (many North Sea sites, 
Galicia, Arcachon Basin). In some sites (United 
Kingdom, Brittany) the intertidal Zostera marina 




form ("Zostera angustifolia") can extend across 
large muddy areas in the mediolittoral belt, 
mainly on poorly drained sediments with a thin 
water layer remaining at the sediment surface 
during the low-tide period. 

) Semi-open habitats under marine conditions 
(salinity of 32-36 psu). These beds occur on sandy 
and locally even on coarse sediments from a 
depth of +2 m mean sea level to -3 m. Their 
spatial extension depends on the rocky platforms, 
small islands and hard substrate structures 
which protect the beds from the most extreme 
hydrodynamic forces {strong currents, swell and 
waves]. This type is common along the western 
coasts of the Channel. 

) Open habitats under fully marine and subtidal 
conditions [-2 to -10 m mean sea level) mainly 
around islands in very clear waters. Swell is 
probably the main factor limiting the extension of 
these beds to the intertidal zone. Zostera marina 
can occasionally be observed in artificial lagoons, 
brackish pools and abandoned salt production 
areas on the French Atlantic coast!” with a 
morphology close to its intertidal morph. 

Zostera noltii is very often found in estuarine and 
sheltered environments as described above but 
occupies higher levels on the shore. The species mainly 
occurs in muddy and sandy sediments and can form 
extensive beds on tidal flat areas [Wadden Sea, United 
Kingdom, Ireland, Gulf of Morbihan and Arcachon 
Basin). The species is never found below the low-tide 

The primary production of Zostera marina meadows is 
the highest of the coastal sedimentary environments of 
the region. The associated organisms supported by 
eelgrass production are numerous and diverse. The 
beds are used as refuge and nursery areas by many 
species, including commercial fish and invertebrates. 
At this latitude, growth of the perennial morph is 
continuous throughout the year, although limited in 
winter, so there is a permanent flux of seagrass tissues 
inducing a detritus-based food chain. The detritus often 
becomes accumulated by waves and tidal currents 
outside the beds which thus spatially extend their 
functional role in the marine ecosystem". It has been 
calculated that 1 g (dry weight) of seagrass detritus 
supports on average 9 mg of bacteria and protists”’. 
The living leaves are used as a Substrate by diatoms, 
bacteria and heterotrophic protists and many macro- 
epiphytes (algae and invertebrates). 

The total surface area available for the superficial 

biofilm and epiphytes, calculated by adding the surface 
area of all the leaves of the shoots, can reach 6 to 8 m’ 
in 1m? of sediment [leaf area index]. Whelan and 
Cullinane’ identified 60 algal species in Ventry Bay 
(Ireland) and Connan and Hily'“’ found 82 epiphytic 
algal species in Brittany beds including 60 species in 
only one bed in the Bay of Brest. Some of these species 
are found only on Zostera leaves, or have their most 
luxuriant development on these, such as the small 
Phaeophytes Ascocyclus magnusii, Myriotrichia 
clavaeformis, Cladosiphon zosterae and Punctaria 
tenuissima, and the Rhodophytes Fosliella lejolisii, 
Erythrotrichia bertholdii, Erythrotrichia boryana and 
Rhodophysema georgii. This epiphytic community, 
described as Fosliello-Myriotrichietum clavaeformis, 
occurs only along the oceanic coasts and is very 
sensitive to pollution. 

In western Europe, many commercial fish and 
shellfish species use eelgrass meadows as a habitat. 
Some fish predators occupy the beds during tidal and 
nocturnal migrations (Labridae, Morone labrax and 
flatfish]. Others use the beds as spawning sites and 
nursery areas (Mullus surmuletus). The juveniles of the 
crab Maja squinado, an important commercial species 
in France, hibernate in the sediments of the subtidal 
beds'’. The beds are actively exploited by handnet 
fishermen for the shrimp Leander serratus. Many 
commercial bivalves such the clams Venerupis 
pullastra, Venus verrucosa, razor shells, Lutraria 
lutraria, and pectinids, Chlamys opercularis and 
Pecten maximus, are especially abundant in the 
Zostera marina beds and are heavily exploited for 
recreational fishing. 

Some rare and endangered species like the sea 
horse (Hippocampus sp.) still occur in Zostera marina 
beds in the area. A few invertebrates directly consume 
the eelgrass leaves, e.g. the sea urchin Sphaerechinus 
granularis and the sea rabbit Aplysia punctata. Brent 
geese (Branta bernicla) used to be strongly dependent 
on the eelgrass meadows (Zostera noltii and Zostera 
marina) which are generally found in their main 
migration sites. At present they have found alternative 
food sources following the loss of eelgrass. Other birds 
such as teal, widgeon, pintail, mallard, shoveler, 
pochard, mute swan and coot are also consumers of 


Before the outbreak of the wasting disease in the 1930s, 
eelgrass beds were very common along the European 
coasts. The beds were locally harvested for different 
uses (soil improvement (Galicia, Spain), embankment or 
dikes around fields on small islands (Brittany, France], 
sea walls [the Netherlands), filling of mattresses and 
cushions (Normandy, France, the Netherlands], 

packaging, roofing and insulation material); therefore 
eelgrass was historically of economic importance. As an 
example, about 150 km’ were covered by eelgrass in the 
western Wadden Sea'””!. Despite this abundance, already 
by the 18th century, Martinet'”’’ was urging development 
of a method to multiply eelgrass, because “one cannot 
have too much of it””"”. Though little documentation is 
available, it seems that Zostera marina was more 
abundant than Zostera noltii. Most of the subtidal 
Zostera marina beds did not recover from the wasting 

Case Study 2.1 

The Wadden Sea is one of the world’s largest 
international marine wetland reserves. Before the 
1930s it contained large beds of subtidal and low- 
intertidal Zostera marina, whereas many mid- 
intertidal flats were covered with a mixed bed of 
Zostera marina and Zostera noltii. After the wasting 
disease in the 1930s, seagrasses survived only in the 
mid-intertidal zone (a narrow zone around 0 m mean 
sea level}. Here, new losses occurred from the 1970s 
onwards. Increased turbidity, increased shell- 
fisheries, increased construction activities and in- 
creased nutrient loads are the main factors that have 

caused the losses and lack of recovery, although the 
causes of the wasting disease losses during the 
1930s are still open to dispute 

Currently, Dutch seagrass beds cover 2 km’, 
German seagrass beds 170 km* and Danish 
seagrass beds some 30 km’. In the Netherlands, an 

{20, 37) 

intensive monitoring program has revealed large 
fluctuations in cover of Zostera marina particularly: 
for example a sixfold increase in area was observed 
within two years [followed by some decrease], 
whereas at another area an 80 percent decrease was 
observed between two different years (followed by 
some increase]. The Zostera noltii bed cover 
fluctuates less than twofold, which may be ascribed 
to some habitat characteristics, including firm clay 
banks, and the plants’ perennial reproductive 
strategy. The Zostera marina beds in the Wadden 
Sea are mainly {but not totally) annual. These 
fluctuations in cover make the populations 
vulnerable to local and temporal disturbances, 
caused by human actions or by ice scour or gales, 
particularly when the area becomes small, and the 
habitat offers no local refugia. 

Since 1987, the University of Nijmegen, 
assigned by and in cooperation with the Dutch 
Government, has investigated the possibilities for 
restoration of Zostera marina in the western Wadden 

Western Europe 

disease. From the 1960s onwards the eulittoral beds of 
Zostera marina and Zostera noltii declined, probably as 
a consequence of increased turbidity’. In one site the 
increased turbidity was found to be more related to 
increased sediment particles, dredging and filling 
activities than to increased phytoplankton. 

Without doubt, the losses of areas occupied by eelgrass 
have been very great since the beginning of the 20th 

Sea. Water clarity of the Dutch Wadden Sea has 
improved and shellfisheries have been locally 
prohibited. Experiments in the field, in outdoor 
mesocosms and in the laboratory, as well as 
literature, long-term environmental data and global 
information system [GIS] studies, all provided 
knowledge of suitable donor populations, habitat 
requirements and potential habitats®” *** |n 2002, 
transplanting began in the western Wadden Sea. 
Risks will be spread in space and time, the 
transplants will be protected in the field during the 
first years (to prevent seed-bearing shoots drifting to 
open sea} and protective mussel ridges will be 
constructed to provide refugia for the transplants. 

Photo: M. van Katwijk 



Photo: M. van Katwijk 


century in western Europe. After the wasting disease in 
the 1930s which destroyed most of the Zostera marina 
beds, the recovery was very slow and at many sites 
eelgrass did not recover at all. From the 150 km’ in the 
western Wadden Sea estimated to be covered by 
seagrass in 1919 by van Goor'™”, the area estimate in 
1971 was reduced to 5 km? only in intertidal areas!” 
and the beds were estimated to cover approximately 
2 km? in 1994, mainly consisting of Zostera noltii*". 
Giesen" considered that in 1990 Zostera marina had 
declined to the point of virtual disappearance in the 
Dutch Wadden Sea; at present only two locations of this 
species are still known in the area. 

In a few cases, anthropogenic shoreline 

modifications have facilitated the growth of eelgrass 
beds. In the second part of the 20th century several 

Aerial photograph showing the impact of shellfisheries on an 
intertidal Zostera noltii bed 

large constructions along the coast of the Netherlands 
modified the sites colonized by eelgrass. The 
construction of a dam in 1964, 25 km upstream of the 
Grevelingen Estuary, isolated the ecosystem from the 
freshwater influence; at that period the eelgrass beds 
covered about 12 km‘? in the intertidal belt. Then, in 
1971, a second dam at the mouth of the estuary isolated 
the system from the sea’s influence. The Grevelingen 
Estuary was transformed into a stagnant salt water 
lake. The new conditions favored the extension of the 
Zostera marina beds, which became permanently 
submerged, and occupied about 34 km’ in the period 
1971-85". Zostera noltii, which was the most common 

seagrass before this human intervention, declined to 
almost complete disappearance; in the early 1990s a 
small, completely submerged stand of a few square 
meters was found in very shallow water. The extension 
of the Zostera marina beds soon came to a halt. A 
large-scale die-off started around 1986-87, and has so 
far not been explained in a convincing way” *". 

Most of the recent observations underline, 
however, the gradual regression of the eelgrass bed 
areas under anthropogenic influence. Human impact 
may be exercised directly by dredging, filling and mar- 
ina development, aquaculture of mollusks (Ostreidae, 
Mytilidae, Veneridae) and fish farms, anchoring and 
other boat activities, and directly and indirectly by the 
effects of eutrophication, such as increasing turbidity, 
development of invasive macroalgae and floating 
blankets of macroalgae which may suffocate the 
seagrasses, and development of high biomass of 
epiphytic microalgae and macroalgae on the leaves. In 
the geographic area considered, the intensity of these 
perturbations varies from one region to the other. 

Along the Channel coasts the natural harbors are 
used as semi-permanent anchoring sites for pleasure 
boats as here the optimal conditions for this activity, 
including tidal level considerations, protection from 
swell and currents, and distance from the shore are 
met. Unfortunately, these are exactly the sites where 
Zostera marina has its ecological optimum. This 
activity is an important cause of the erosion of eelgrass 
beds and it is increasing very rapidly everywhere. In the 
same way, recreational fishing is increasing; the 
digging of mollusks during low tide at spring tides by 
very destructive tools induces a rapid regression of the 
intertidal parts of Zostera marina beds. Numerous 
eelgrass sites of Zostera noltii and Zostera marina are 
progressively disappearing with the rapid extension of 
aquaculture, in France and Spain, on intertidal sites. In 
Cornwall and Devon (southern England) many losses 
were pointed out by Giesen”’ by comparing the results 
given by Covey and Hocking’, and Holme and Turk”; 
no explanations were found for these losses. The less- 
threatened beds are probably the deeper subtidal 
Zostera marina meadows under semi-exposed 
conditions particularly around small islands, but the 
continuously increasing turbidity of the coastal waters 
in western Europe, generally recognized but not really 
quantified, is probably a factor in the variations of the 
lower limits observed in many beds. As an example, 
the lower limit of Zostera marina in Ventry Bay [Ireland] 
was 13 m in 1977-78, 10 m in 1980 and continued to fall 
after 1980". 

The loss of eelgrass has not been quantified for 
the whole region, but probably more than 50 percent of 
the beds are subject to one or other of the types of 
perturbations mentioned, and are threatened by total 

or partial destruction over the next ten years. A review 
of the abundant literature concerning eelgrass in 
western Europe suggests that the general trend of 
recovery after the almost complete disappearance of 
the sublittoral beds in the 1930s is largely being 
reversed by the diverse, and generally adverse, local 
and regional anthropogenic impacts. 


In France, along the Channel and Atlantic coasts, most 
of the eelgrass sites are known. Along the western 
coast of the Cotentin Peninsula, beds of Zostera marina 
occur near Granville, and the most eastern beds of 
Zostera noltii are in Baie des Veys near Isigny on the 
eastern side of the peninsula’. Eelgrass beds in 
Brittany were located and mapped in 1999 by Hily et 
al." although the exact area of each bed has not been 
determined. This study identified more than 70 sites 
from the Mont St Michel Bay in the north to the Loire 
Estuary in the south of Brittany. Most of them are small 
beds between 1 and 5 ha, but there are at least ten 
large beds covering 10 to more than 100 ha (including 
the Gulf of Morbihan, Glénan Archipelago, lle de Batz, 
Bay of Brest, Brehat Archipelago, Abers Estuaries and 
Etel Ria). To the south, the Marennes-Oléron Basin is a 
large site of Zostera noltii. Further to the south the 
Arcachon Basin is the largest site of Zostera noltii (70 
km? in 1984] in Europe, and also a large site of Zostera 
marina (4 km? in 1984)”. 

In the United Kingdom, most of the beds are 
mapped and consist of about 140 sites of Zostera 
marina [including the intertidal sites) and about 70 
sites of Zostera noltii'”. Some of them extend over a 
considerable area, such as the Zostera marina bed in 
the Cromarty Firth, Scotland, which covers 12 km’! 
and is considered the largest bed in the United 
Kingdom. In the cross-border sites of Scotland and 
England, the Solway Firth and the northern 
Northumberland coasts have coverage respectively of 
2 and 9 km’: * Along the coast of England, the 
seagrass coverage of some large sites has been 
documented: Essex estuaries (8.44 km’], North Thames 
Estuary (3.25 km’J, Solent and Isle of Wight (4.40 km’), 
Plymouth Sound and estuaries (6.50 km‘). Some 
smaller beds occur in Devon and Cornwall. In Wales, 
the main sites are in the Lleyn Peninsula and the 
Sarnau, while in Northern Ireland the beds in the 
Strangford Lough cover 6.30 km’"!. Zostera marina 
beds are also common on the semi-sheltered 
sediments of the Channel Islands. 

Along the southeastern coasts of the North Sea, 
seagrass beds are restricted to the sheltered Wadden 
Sea and southwest Netherlands and cover a total of 
200 km’. 

In Spain, the actual seagrass coverage is not 

known, but many beds are recorded from the numerous 
rias of the Galicia region (Zostera noltii covers 
approximately 20 km* between the French and 
Portuguese coasts'"). In Portugal, the Ria Formosa is 
recorded as a site for intertidal Zostera nolti/ beds and 
subtidal beds of Zostera marina and Cymodocea 

It is at present not possible to measure the 
potential seagrass habitat in the whole region. 
However, it can be estimated that it would be more than 
three times the actual coverage both for Zostera 
marina and Zostera noltii. An estimate for Brittany is 
planned in 2003 with a long-term survey of the coastal 
benthic communities (REBENT network survey) 
including Zostera beds. In the United Kingdom the 
Habitat Action Plan for seagrass beds developed by the 
UK Biodiversity Steering Group may result in quite an 
accurate estimate of the potential habitat in this area. 


Direct destruction of beds 

As a result of the rapid development of pleasure fishing 
and sailing over the last 20 years, filling and dredging 
for extension or creation of harbors have destroyed 
many eelgrass beds. As a consequence of economic 
and environmental arguments such developments are 
becoming less harmful nowadays, but the damage has 
been done. 

Oyster and mussel aquaculture on littoral 
sediments has been the cause of the destruction of 
many eelgrass beds because the optimal conditions for 
the culture of these animals correspond with the 
optimal conditions for the beds. This activity is still 
expanding, and will probably be one of the main threats 
to the beds in the future. 

Anchoring and mooring outside harbors is 
damaging. Anchoring causes the formation of deep 
holes which in their turn may become points of impact 
for the eroding forces, while the chains dragging across 
the bottom destroy the surrounding biocenoses 
including the seagrass communities. 

Hand fishing for clams using rakes, forks and 
hoes to catch the endofaunal bivalves at low tide, as 
well as within the seagrass beds, results in whole 
plants with their rhizomes being pulled out of the 
sediment. This causes considerable damage to the 
seagrass beds, because it is generally followed by 
erosion. Collecting clams in this way is becoming very 
popular, so this type of perturbation is increasing in 
western Europe. The same kind of perturbation is 
caused in the eulittoral seagrass beds by digging for 
polychaetes such as Arenicola and Nereis to be used 
as bait. 

Professional fishermen on boats dredge on the 
limits of the beds to catch bivalves. The natural 

Western Europe 43 



acclimation of the Japanese clam  Venerupis 
philippinarum in the south of the area [from south 
Brittany to Spain) increases the direct impact of this 
activity on the seagrass beds because this species 
develops dense populations in and around the eelgrass 
beds of the sheltered bays and estuaries'. In the 
Netherlands, much damage has been done to the few 
still existing eelgrass beds by professional cockle 
fisheries with their modern, effective, but environ- 
mentally unfriendly equipment. 

Indirect destruction of beds 

Eutrophication is the main cause of indirect destruction 
of seagrass beds. The increase of organic matter and 
nutrients from terrestrial effluents favors phyto- 
plankton, causing blooms which in their turn decrease 
light availability. Moreover, plankton production 
increases not only in terms of instantaneous biomass 
but the period of production also becomes longer and 
longer, and can be observed all year in some areas with 
numerous successive small blooms”. As a cons- 
equence of these plankton blooms, the water trans- 
parency decreases, limiting the light available for the 
growth of Zostera. 

Apart from this shading effect by plankton, a 
further reduction of light is brought about by increased 
epiphyte cover on Zostera leaves in which both diatoms 
and macroalgae participate. The specific community of 
small epiphytes mentioned above is, however, the first 
element to disappear from the seagrass bed in the case 
of eutrophication. Eutrophication also increases the 
production of green macroalgae (Enteromorpha, Ulva); 
particularly in semi-enclosed, sheltered bays the green 
algae can form thick blankets which float around and 
can be deposited on the Zostera beds of the sandy and 
muddy intertidal flats during periods of very calm 
weather. Under such conditions the seagrass beds 
become smothered and suffocated, leading to complete 
die-off within a very short time“. When these blankets 
are deposited on the bare surface of the intertidal flats, 
the spatial competition favors the green algae which 
prevent the extension of the seagrass beds, and reduce 
the growth of shoots by shading and suffocation effects 
in the areas where they border the seagrass beds. In 
these conditions the beds decrease progressively, and 
may completely disappear in a few years. 

The increase of turbidity is not only associated 
with eutrophication, but can also result from an 
increasing input of terrigenous particles by river 
effluents as a consequence of large-scale changes in 
agricultural practices; modern practices encourage the 
leaching of soil in winter. Extraction of calcareous 
sediments and calcareous macroalgae (Lithophyllum 
sp.) from sublittoral beds induces high turbidity; the 
high levels of sediment in suspension in the water 

reduce light and cover the leaves of seagrass during 
resedimentation. Dredging for harbor and channel 
maintenance and releasing the dredged sediments on 
the seafloor also increases turbidity and lowered light 

Spatial competition with invasive species may 
also limit the extension of seagrass beds in western 
Europe. The brown algae Sargassum muticum is able 
to develop in the eelgrass beds where the sediment 
floor is coarse or includes gravel, stones and/or shells. 
In these beds Sargassum gradually takes over and 
prevents the rejuvenation of eelgrass”. 

Most of these threats concern the eelgrass 
Zostera marina. The intertidal species Zostera noltii 
has been assumed to be threatened by a combination of 
various factors including turbidity, eutrophication and 
associated epiphyte cover, the decrease of mud snail 
populations (Hydrobia ulvae) which graze on the 
epiphytes, and also as a result of bioturbation by the 
lugworm Arenicola marina. These processes have been 
well studied in the Dutch Wadden Sea by Philippart'””. 

Finally, a very important potential threat is 
shipping. The Channel and the southern North Sea are 
among the world’s busiest shipping routes and the 
chance that accidents will occur cannot be excluded 
{adverse weather conditions; human error). Notorious 
disasters were those with the tankers Torrey Canyon 
and Amoco Cadiz in the western Channel and recently 
Erika in North Biscay. The impact of these oil spills on 
the whole coastal ecosystem has been disastrous. 

The European Union (EU) elaborated a Habitats 
Directive for both terrestrial and marine habitats which 
identifies the main natural habitats and their cultural 
value for further consideration in terms of protection 
and conservation. In this context eelgrass beds are 
identified as particular ecological units of several 
marine habitats: sandy shore, mud flats and coastal 
subtidal sandy sediments. These initiatives have led to 
eelgrass habitats being specifically targeted for 
conservation and restoration™’. But although they are 
considered as biotopes of special interest, they are not 
considered as “endangered” and so not considered for 
immediate and strong protection. In France Zostera 
marina is listed in the Red Book of threatened species 
but is not in the list of protected species. Zostera noltii 
is not considered. Additionally, very locally and in few 
localities, some Zostera beds are protected by 
municipal authorities. In March 2002, Zostera marina 
and Zostera noltii were both incorporated in the Dutch 
Red List of threatened plants. 

In the United Kingdom, the eelgrass beds have 
been considered for many years as targets for 
conservation and a habitat action plan for seagrass 

Case Study 2.2 

In the northern part of the Bay of Biscay, the Glénan 
Isles are located 9 miles off the continental coast of 
south Brittany, France. The area is characterized by 
ten small islands and numerous rocky islets 
surrounding an enclosed, shallow [<5m deep), 
sandy area well protected from the oceanic swell. 
Aerial photographs are available from the year 1932 
and allowed estimates of the long-term develop- 
ment of the areas covered by eelgrass”. 

This is an interesting experimental site be- 
cause the continental influence (eutrophication and 
associated consequences) is minimized which 
allows the observation of the natural dynamics of the 
beds under climatic factors, but also because 
human activities (anchoring, fishing) induce local 
perturbations in the eelgrass beds. So it is possible 
to separate the role of each of the factors that 
control the dynamics. 

Based on the cover in 1932, it can be 
considered that a surface of 10 km‘ is suitable for 
eelgrass beds, but in 1990 only 25 percent of this 
area was colonized by eelgrass. In 2000, this percen- 
tage increased to around 40 percent as a result of 
positive climatic conditions since 1995; this tendency 
is also observed in many beds of the Brittany 
coasts! However this evolution is moderated by the 
negative impacts of numerous human activities”: 
fo) dredging for clams by professional fishing 

boats prevents recolonization in the opened 

central subtidal part of the area; 

anchoring by numerous pleasure boats 

Anchoring on a Zostera marina bed in Glénan Archipelago. 

Western Europe 

throughout the year induces fragmentation of 
the beds in five main sheltered subtidal sites; 
recreational fishing for clams induces 
fragmentation of the intertidal beds; 
extraction of calcareous sediments {maerl 
beds) 1.5 miles off the archipelago induces 
heavy turbidity in the northern waters of the 
archipelago which may limit the extension of 
the beds in depth la decrease of the deeper 
limits of the laminarians close to the beds was 
recently demonstrated""). 

This example underlines the complexity of the 
dynamics of the eelgrass beds which are under the 
influence of factors working at various spatial and 
temporal scales: here the positive climatic factors 
working at the global scale compensate for the 
negative impacts of the perturbations induced by 
human activities at the local scale. 

This example also underlines the difficulties of 
seagrass conservation: it is hard to explain to the 
authorities and users alike that human activities 
must be moderated in the beds because of their 
impacts while the spatial cover is actually 
increasing. It is necessary to explain that under 
adverse climatic conditions [which are expected in 
the future) the cumulative effect, with human 
impacts, would induce dramatic and rapid loss of 
the beds, and consequently preventive action should 
be planned. 

Fortunately, the management authorities at 
this site are working with the scientific teams on a 
sustainable development plan to preserve the image 
of high environmental quality in this tourist area. 

Photo: C. Hily 


Photo: C. Hily 


Zostera marina on a maerl bed in the Bay of Brest 

beds was prepared by the UK Biodiversity Steering 
Group. In a complementary way, the South West 
Regional Biodiversity Habitat Action Plan has also been 
developed. These initiatives are integrated in the EU 
Habitats Directive which requires the identification of 
European marine sites in a network called “Natura 
2000": sites which should be managed in order to 
maintain or restore the favorable conservation status of 
their habitats and species. Each state of the EU has the 
statutory responsibility, via the conservation agencies, 
for developing conservation objectives in each site, 
defined as a statement of the nature conservation 
aspirations fora site. In the United Kingdom these sites 
are called SACs (special areas of conservation), in 


1 den Hartog C [1981]. Aquatic plant communities of poikilosaline 
waters. Hydrobiologia 81: 15-22. 

2 den Hartog C [1983]. Structural uniformity and diversity in Zostera- 
dominated communities in western Europe. Marine Technology 
Society Journal 17: 105-117. 

3 Hily C, Bouteille M [1999]. Modifications of the specific diversity and 
feeding guilds in an intertidal sediment colonized by an eelgrass 
meadow (Zostera marina] (Brittany, France). Comptes Rendus de 
UAcadémie des Sciences Serie Ill, Sciences de la Vie/Life Sciences 
322: 1121-1131. 

4 den Hartog C [1987]. "Wasting disease” and other dynamic 
phenomena in Zostera beds. Aquatic Botany 27: 3-13. 

5 Giesen W [1990]. "Wasting Disease” and Present Eelgrass 
Condition. Report to Dutch Ministry of Transport and Waterways. 
University of Nijmegen, Netherlands. 138 pp. 

France they are called “sites Natura 2000". The 
regulations suggest that relevant authorities from the 
various sites should work together within a 
management group. In most countries, the presence of 
Zostera beds has been a criterion (but not the only one] 
to retain a site as a SAC. When a bed is included ina 
SAC, specific management is required for the bed. This 
procedure is to be applied independently by each 
country, and has not yet been achieved. Some sites 
derive their conservation status from a combination of 
several different directives, and this can reinforce the 
conservation of Zostera beds. For example, some sites 
are also RAMSAR sites and/or sites of the EU Birds 
Directive, which reinforces the international recognition 
of the site's importance and requires the government to 
strongly protect the site. However, the sites indicated 
according to these directives are far from covering all 
the eelgrass beds in Europe. It therefore remains very 
important to give global consideration to eelgrass 
habitats on a wide scale and it remains necessary to 
define specific conservation regulations at the level of 
the species or genus and/or the habitat. 


Dr R.M. Asmus kindly provided Zostera marina cover percentages for the 
German Wadden Sea. Thanks to Ingrid Peuziat who provided data on the 
Glenan Archipelago. 


Christian Hily, Institut Universitaire Européen de la Mer (University of 
western Brittany], Technopole Brest Iroise, 29280, Plouzane, France. 
Tel: +33 (0)2 98 49 86 40. Fax: +33 (0)2 98 49 86 45. E-mail: 
christian. hily( 

Marieke M. van Katwijk, Department of Environmental Studies, University 
of Nijmegen, P.O. Box 9010, 6500GL Nijmegen, Netherlands. 

Cornelius den Hartog, Department of Aquatic Ecology and Environmental 
Biology, University of Nijmegen, P.0. Box 9010, 6500GL Nijmegen, 

6 Davison DM, Hughes DJ [1998]. Zostera Biotopes: An Overview of 
Dynamics and Sensitivity Characteristics for Conservation 
Management of Marine SACs. Reports UK Marine SACs Project, 
Task Manager, AMMW Wilson, SAMS. 95 pp. 

7 Stewart A, Pearman DA, Preston CD [1994]. Scarce Plants in 
Britain. JNCC, Peterborough. 

8 Whelan PM [1986]. The Genus Zostera in Ireland. PhD thesis, 
University College Cork, Ireland. 215 pp. 

9 Whelan PM, Cullinane JP [1987]. The occurrence of “wasting 

disease” of Zostera marina in Ireland in the 1930s. Aquatic Botany 

27: 285-289. 

Hily C, Raffin C, Connan C [1999]. Les herbiers de zostéres en 

Bretagne: Inventaire des sites, faune et flore. Rapport Diren Region 

Bretagne, Universite de Bretagne Occidentale, Brest. 57 pp. 

Curras A, Sanchez-Mata A, Mora J [1993]. Estudio comparativo de 

la macrofauna bentonica de un fondo de Zostera marina y un fondo 










arenoso libre de cubierta vegetal. Cahiers de Biologie Marine 35: 

Gruet Y [1976]. Répartition des herbiers de Zostera 
(Monocotyledones marines] sur l'estran des cotes de Loire- 
Atlantique et du Nord de la Vendée. Bulletin Société des Sciences 
Naturelles de Ouest de la France 74: 86-90. 

Whelan PM, Cullinane JP [1985]. The algal flora of a subtidal 
Zostera bed in Ventry Bay, south-west Ireland. Aquatic Botany 23: 

Hily C. Personal observations. 

van Goor ACJ [1919]. Het zeegrass (Zostera marina] en zijn 
beteekenis voor het leven der visschen. Rapp Verh Rijksinst 
Visscherij 1[4]: 415-498. 

Martinet JF [1782]. Verhandeling over wier der Zuiderzee. 
Verhandelingen Hollandsche Maatschappij der Wetenschappen 20: 

van Katwijk MM [2000]. Possibilities for Restoration of Z. marina 
Beds in the Dutch Wadden Sea. PhD thesis, University of Nijmegen, 
Netherlands. 160 pp. 

de Jonge VN, de Jong DJ [1992]. Role of tide, light and fisheries in 
the decline of Zostera marina in the Dutch Wadden Sea. 
Netherlands Institute for Sea Research Publications Series 20: 

den Hartog C, Polderman PJG [1975]. Changes in the seagrass 
populations of the Dutch Waddenzee. Aquatic Botany 1: 141-147. 
Philippart CJM [1994]. Eutrophication as a Possible Cause of 
Decline in the Seagrass Zostera noltii of the Dutch Wadden Sea. 
PhD thesis, University of Wageningen, Netherlands. 157 pp. 
Dijkema KS, van Tienen G, van Beek JG [1989]. Habitats of the 
Netherlands, German and Danish Wadden Sea 1:100,000. Research 
Institute for Nature Management, Texel and Veth Foundation, 

Nienhuis PH, de Bree BHH, Herman PMJ, Holland AMB, 
Verschuure JM, Wessel EGJ [1996]. Twenty-five years of changes in 
the distribution and biomass of eelgrass, Zostera marina, in 
Grevelingen Lagoon, the Netherlands. Netherlands Journal of 
Aquatic Ecology 30: 107-117. 

Herman PMJ, Hemminga MA, Nienhuis PH, Verschuure JM, Wessel 
EGJ [1996]. Wax and wane of eelgrass Zostera marina and water 
column silicon levels. Marine Ecology Progress Series 144: 303-307. 
Covey R, Hocking S [1987]. Helford River Survey. A report to the 
Helford River Steering Group. 121 pp. 

Holme NA, Turk SM [1986]. Studies on the marine life of the 
Helford River: Fauna records up to 1910. Cornish Biological 
Records No. 9. 26 pp. 

Le Gall J, Larsonneur C [1972]. Sequences et environnements 



















Western Europe 

sédimentaires dans la Baie des Veys [Manche]. Revue de 
Géographie Physique et Geologie Dynamique 14: 189-204. 

Auby | [1991]. Contribution a l'etude des herbiers de Zostera noltii 
dans le bassin ‘Arcachon: Dynamique, production et dégradation, 
macrofaune associée. These de doctorat, Universite de Bordeaux. 
234 pp. 

RSPB [1995] Annual Report of the Royal Society for the Protection 
of Birds. RSPB, Sandy, Bedfordshire. 

Hawker D [1993]. Eelgrass in the Solway Firth. Report for Scottish 
Natural Heritage. 

Percival SM, Sutherland WJ, Evans PR [1997]. Intertidal habitat loss 
and wildfowl numbers: Application of a spatial depletion model. 
Journal of Applied Ecology 35(1): 57-63. 

Laborda AJ, Cimadevilla |, Capdevila L, Garcia JR [1997]. 
Distribucion de las praderras de Zostera noltii Hornem., 1832 en el 
litoral del norde de Espana. Publ Espec Inst Esp Oceanogr 23: 273- 

den Hartog C, Hily C [1997]. Les herbiers de Zosteéres. In: Dauvin 
JC (ed) Les Biocénoses marines et littorales francaises des cotes 
Atlantiques Manche et Mer du Nord: Synthese, menaces et 
perspectives. MNHN, Paris. pp 140-144. 

Chauvaud L, Jean F, Ragueneau 0, Thouzeau G [2000]. Long-term 
variation of the Bay of Brest ecosystem: Benthic-pelagic coupling 
revisited. Marine Ecology Progress Series 200: 35-48. 

den Hartog C [1994]. Suffocation of a littoral Zostera bed by 
Enteromorpha radiata. Aquatic Botany 47: 21-38. 

den Hartog C [1997]. ls Sargassum muticum a threat to eelgrass 
beds? Aquatic Botany 58: 37-41. 

Wynne DW, Avery M, Campbell L, Gubbay S, Hawkswell S, Juniper 
T, King M, Newbery P, Smart J, Steel C, Stones T, Taylor J, 
Tydeman C, Wynde R [1995]. Proposed targets for habitat 
conservation. In: Biodiversity Challenge. 2nd edn. RSPB, Sandy, 
Bedfordshire. 285 pp. 

van Katwiijk MM, Hermuus DCR, de Jong DJ, Asmus RM, de Jonge 
VN [2000]. Habitat suitability of the Wadden Sea for restoration of 
Zostera marina beds. Helgoland Marine Research 54: 117-128. 
van Katwiijk MM, Schmitz GHW, Gasseling AP, Van Avesaath PH 
[1999]. Effects of salinity and nutrient load and their interaction on 
Zostera marina. Marine Ecology Progress Series 190: 155-165. 
Giesen WBJT, van Katwijk MM, den Hartog C [1990]. Eelgrass 
condition and turbidity in the Dutch Wadden Sea. Aquatic Botany 
37: 71-85. 

Glémarec M, Le Faou Y, Cug F [1996]. Long-term changes of 
seagrass beds in the Glenan Archipelago (South Brittany). 
Oceanologica Acta 20(1): 217-227. 

Castric A. Personal communication. 




3 The seagrasses of 


date back to the beginning of the 19th century, 

when the most widespread and well-known 
species, Posidonia oceanica, was described for the first 
time. Since then thousands of papers have detailed 
different aspects of seagrass distribution, ecology, 
physiology, faunal and algal assemblages and, recently, 
genetics. Two international workshops in the early 
1980s were dedicated to the endemic Posidonia 
oceanica and led to joint research programs among 
European countries to study the structure and 
functioning of the Posidonia oceanica ecosystem. Less 
information exists on the other Mediterranean 
seagrass species, although some of them are quite 
common and widespread in the basin. A significant 
contribution to the synthesis of the work conducted on 
Mediterranean seagrasses was offered by the 
organization of the Fourth International Seagrass 
Biology Workshop held in Corsica in 2000". 

Give on seagrasses in the Mediterranean basin 


Six seagrass species are present in the Mediterranean 
Sea, forming an almost continuous belt all along the 
coasts: Posidonia oceanica; Cymodocea nodosa, also 
present along the North Atlantic African coasts and 
Portugal; Zostera marina and Zostera noltii, both with 
a wide temperate distribution; Halophila stipulacea, 
probably a recent introduction from the Red Sea; and 
Ruppia spp., with a wide temperate distribution (Table 
3.1). Extremely limited information is available on 
Ruppia in the Mediterranean and it will not be 
considered further. 

Posidonia oceanica forms continuous meadows 
from the surface to a maximum depth of some 45 m and 
is common on different types of substrate, from rocks to 
sand, with the exception of estuaries where the input of 
freshwater and fine sediment is high. Posidonia oceanica 
beds have classically been considered one of the climax 


G. Procaccini 

M.C. Buia 

M.C. Gambi 

M. Perez 

G. Pergent 

C. Pergent-Martini 

J. Romero 

communities of the Mediterranean coastal area’. 
Meadows are very dense with over 1000 shoots/m? 
although this varies from year to year“. The horizontal 
and vertical growth of rhizomes, and the slow decay of 
this material, causes Posidonia oceanica to form a 
biogenic structure called “matte”, that arises from the 
bottom up to a few meters and can be thousands of years 
old". Posidonia oceanica is a monoecious species, with 
male and female flowers in the same inflorescence. 
Sexual reproduction is sporadic, especially in some 
areas. Posidonia oceanica has low genetic variability and 
meadows represent genetically distinct populations, 
even at a scale of a few kilometers”. A clear genetic 
distinction exists between northwestern, southwestern 
and eastern populations. Meadows are composed of a 
mosaic of large and ancient clones”. 

Cymodocea nodosa most commonly occurs in 
shallow water but exceptionally can reach a depth of 
30-40 m. Shallow and deep stands are generally 
discontinuous. Cymodocea nodosa is usually found on 
sandy substrate and sheltered sites". In France, the 
most important beds are known in coastal lagoons. 
Shoot density reaches almost 2000 shoots/m’*". It has 
classically been considered to be a pioneer species in 
the succession leading to a Posidonia oceanica climax 
system. However it also grows in areas previously 
colonized by Posidonia oceanica and characterized by 
dead matte. Cymodocea nodosa is a dioecious species. 
Seeds remain for a long time in the sediment, attached 
to the mother plant. The only existing analysis of 
Mediterranean meadows showed high genetic diversity. 
In fact, plants 5 m apart within a meadow were 
genetically distinct individuals”. 

Zostera marina is considered to be a relict 
species in the Mediterranean, where it forms perennial 
meadows distributed from the intertidal to a few 
meters deep. It can grow on sandy and muddy 
substrate and is also present in lagoons", though it is 


Medes Is. 

- Catalan 

Alfacs Bay 

<> . 

Balearic Islands 



The western Mediterranean 

, sa Gulf of Trieste. 



@Numana » * 

FRANCE Uguria” ~ Venice Lagoon — 
Pete game o*s 
- Po River 

- A5°N 
Delta 5 




Corsica ITALY 

bs Apulla’ A DRIATIC 


se Ischia L* 




0 100 200 300 Kilometers eb cene 
Le 35° y 

Map 3.1 
The western Mediterranean 

rare throughout the Mediterranean. Shoot density in 
Zostera marina beds is almost 1000 shoots/m?""". 
Zostera marina is a monoecious plant. Studies on the 
genetic diversity of this species have never been 
performed in the Mediterranean. 

Zostera noltii grows from the intertidal to depths 
of a few meters on sandy and muddy substrate”. It is 
also present in enclosed and sheltered areas, where it 
can form mixed beds with Cymodocea nodosa, at 
densities up to almost 1300 shoots/m’. Zostera noltii is 
a monoecious species and no information is available 
about the genetic variability of its populations. 

Table 3.1 

Examples of general features of Mediterranean seagrass meadows 



6 526 324 
7-147 3-21.3 
0.077-0.4 - 




Density (shoots/m’) 

Leaf area index {m’/m*] 
Leaf biomass (g dw/m’} 
Below biomass (g dw/m’) 
Epiphyte biomass (g dw/m’ 
Animal biomass (g dw/m?) 
Number of algal species 36 50 
Number of animal species 38-60 22-84 
Animal density (individuals/m*) 380-1 100 210-680 
Leaf production (g dw/m7/y] 162-722 71.3-232 
Rhizome elongation (cm/y) 1.1-7.4 
Leaf lifespan [months] 11 








1 486 
1 623 





Halophila stipulacea was recently introduced to 
the western Mediterranean Sea and was reported for 
the first time in 1988. In the eastern Mediterranean 
basin this species has been observed from the 
beginning of the 19th century and Is believed to have 
been transported from the Red Sea, through the Suez 
Canal, an example of Lessepsian migration. In the 
Mediterranean it is distributed from the intertidal zone 
to 25 m'”!. It can grow on sandy and muddy substrate, 
and is present in enclosed areas. Shoot density is 
extremely high, up to almost 19000 shoots/m? in 
shallow water”. Halophila stipulacea is a dioecious 



shallow deep 

19728 13000 
5 5.9 0.2-0.4 
157.8 - 13-79 45-775 
- 31-62 21-161 

- 0.7-3.2 



269-1 246 


Source: Modified from Buia et al”. Values derived from key studies listed in Buia et al 



Photo: Laboratory of Benthic Ecology (SZN) 

Case Study 3.1 


The Ligurian area is one of the best among the 
Italian coasts for information on the distribution 
and general status of seagrasses, in particular for 
Posidonia oceanica. Almost 50 Posidonia oceanica 
main meadows have been recorded and 
mapped”. Their extension ranges from a few to 
several hundred hectares, covering in total about 
48 km’. In general all the prairies are in different 
states of degradation due to coastal modifications 
for harbor and town development. In addition 
some Posidonia oceanica beds were impacted in 
the early 1990s by a crude oil spill following the 
wrecking of the oil tanker Haven, considered to be 
one of the worst Mediterranean oil spills" 

Posidonia oceanica banquette on the Cava dell'Isola beach, 
Ischia Island, Italy. 


At a smaller spatial scale, the best-known 
Posidonia oceanica meadows are those 
surrounding the Island of Ischia, in the northern 

part of the Gulf of Naples. Posidonia oceanica 
covers about 17 km’ of the seafloor, and its 
meadows, forming a continuous belt around the 
island, were mapped in detail in 1979! The 
different exposure of the coasts of the island, 
coupled with different environmental conditions 
and bottom type, give rise to meadows extremely 
diversified in terms of physiognomy [continuous 
and patchy beds], depth range [from 0 down to 
38 m in depth], shoot density {from a mean of 900 
shoots/m? at 1 m to 80 shoots/m* at 30 m depth) 
and biodiversity of associated communities (more 
than 800 associated species], and with low 
intrinsic genetic variability, coupled with a degree 
of isolation between shallow and deep stands” 

A recent monitoring of beds around the 
island [in the year 2000) demonstrates a 
substantial stability of distribution and the 
presence of other settlements not previously 
reported. However, long-term studies carried 
out since 1979 in beds off Lacco Ameno have 
detected a reduction in shoot density, as a result of 
anchoring, the impact of the local fishery and a 
nearby wastewater outfall. 

Zostera marina |s present on the Italian coasts of 
the north Adriatic Sea — it was first recorded here 
in the 14th century. Posidonia oceanica has 
experienced a strong decrease in this area, being 
now limited to a few patches in the Gulf of 
Trieste™. The worst decline of Posidonia 
oceanica has occurred in the Venice lagoon. In 
1990 Zostera marina covered an area of 36.5 km’, 
forming pure and continuous beds of 2.4 km? and 
beds mixed with Zostera noltii over the other 34 
km?:4_ Zostera noltii was the most widespread 
species (42.5 km’) and Cymodocea nodosa was 
also present [15.6 km?]. Monitoring results four 
years later from the southern part of the 
lagoon” showed an increase of about 7.6 
percent in the overall extent of seagrass beds, 
but with more Zostera marina {an increase of 
13.5 percent], a decrease of 10.1 percent in 
Cymodocea nodosa and a large decline in 
Zostera noltii (24.7 percent]. The monospecific 
and discontinuous beds have increased while 
mixed species beds have declined. A high survival 
rate for Zostera marina, Cymodocea nodosa and 
Zostera noltii has been achieved in transplanting 
experiments using sods and rhizomes at various 
sites in the lagoon”? 

species. Male flowers are frequent in the 
Mediterranean Sea but female flowers were only 
observed for the first time in 1998, in Sicily'’!. Studies 
on the genetic variability of two populations located 
along the Sicilian coasts showed that each shoot 
represents a genetically distinct individual. Genetic 
relatedness was higher among individuals collected at 
the same depth'”. 


Seagrass ecosystems of the western Mediterranean 
are extremely rich in a number of associated plant and 
animal species. However, complete lists of associated 
species have been compiled only in a few cases, such 
as the Posidonia oceanica and Cymodocea nodosa 
meadows of the island of Ischia, where more than 800 
and 250 species have been listed, respectively’, or in 
the Medes Islands'”’. Posidonia oceanica beds are the 
exclusive habitat for many algal and animal species, 
such as the coralline red algae Pneophyllum fragile 
and Hydrolithon farinosum, the brown algae Castagnea 
cilindrica, Giraudia sphacelarioides and Myrionema 
orbiculare, the bryozoan Electra posidoniae, the 
hydroids Aglaophenia harpago, Sertularia perpusilla, 
Campanularia asymmetrica, Cordylophora pusilla and 
Laomedea angulata’*”. 

Posidonia oceanica meadows are nursery 
grounds for the juveniles of many commercially 
important species of fishes and invertebrates, such as 
several species of the family Sparidae (e.g. Diplodus 
sargus and Diplodus annularis), Serranidae (e.g. 

Case Study 3.2 


A long-term monitoring study of Posidonia 
oceanica beds in the Marseille-Cortiou region has 
recorded fluctuations over the 1883-1987 period, 
and the impact of a sewage treatment plant. In the 
period 1890 to 1898, when a sewage outlet was first 
set up in Marseille, the seagrass bed had reached 
a depth of 30 m and occupied an area of about 
6.32 km*. A number of authors noted loss of 
Posidonia oceanica between 1900 and 1970 as the 
city of Marseille expanded", At the end of the 
1970s the bed covered a smaller area, with a loss 
of 5-6 percent per decade. 

When the wastewater treatment plant was 
set up in 1987, the lower limit of the seagrass bed 
was just 10 m and it included vast stretches of 
dead matte. Since then there have been further, 
much greater, losses amounting to 40 percent of 

The western Mediterranean 

Serranus cabrilla), Labridae {e.g. Coris julis and 
Crenilabrus maculatus) and Scorpaenidae (e.g. 
Scorpaena scrofa and Scorpaena porcus), and the sea 
urchin Paracentrotus lividus. Among the rare or 
endangered associated species are the endemic sea 
star Asterina pancerii, the sea horse Hippocampus 
hippocampus and the bivalve Pinna nobilis: these 
species are protected, in both Italy and France, or are 
included among species requiring a specific legislation 
for protection’. 


Information on the distribution of seagrasses is 
scattered and therefore an estimate of the total area 
covered by seagrasses is difficult to make. However the 
beds in some areas are well known. 

The Italian coastline is 7500 km long, without 
taking into account the numerous small islands 
scattered all around the peninsula. It is almost entirely 
surrounded by seagrass meadows that, considering the 
three most abundant species [Posidonia oceanica, 
Cymodocea nodosa and Zostera noltii), extend from 0.2 
to 45 m. Clearly the potential area covered by seagrass 
is enormous. Some 2 350 km’ of seagrass are known to 
occur in Liguria, Lazio, Sardinia, Veneto and Friuli 
(Table 3.2). France has approximately 1150 km? of 
Posidonia oceanica beds, but estimates for other 
species are not available. On the Mediterranean coasts 
of Spain, some regions have mapped their seagrass 
meadows in great detail allowing an estimate of more 
than 1000 km’ to be made. 

the 1970 area. This is most likely due to the high 
levels of suspended matter, ammonium and 
phosphate coming from the treatment plant. After 
1994, a natural recolonization of Posidonia 
oceanica was observed in certain areas, due to 
increased water clarity. 


Corsican coasts experience low human impact 
with many marine protected areas; almost 
71 percent of the Corsican coastline is still in its 
natural state. Posidonia oceanica beds occupy a 
total surface area of 624 km?"" mainly along the 
eastern side of the island, where the continental 
shelf is very wide. Their distribution is limited on 
the steep and indented west coast. Upper limits 
are generally between 1 and 10 m depth, while 
the lower limit at several sites on the east coast 
is situated below 40 m. The lower limit rises to 
a depth of 15-20 m near large cities such 
as Ajaccio. 



The beds of Posidonia oceanica are among the 
most important Mediterranean ecosystems, and their 
conservation is a high national and international 
priority (e.g. EU Habitats Directive 92/43/CEE, 21 May 
1992}. Posidonia oceanica beds exert a multifunctional 
role within coastal systems, comparable to that of other 
seagrasses in temperate and tropical areas, offering 
substrate for settlement, food availability and shelter, 
as well as participating in key biogeochemical and 
geological processes. 

Table 3.2 

Sites Po Cn Zm Zn Hs Area 
Liguria* v v 48 
Tuscany* v v v = 
Lazio v v v 200 
Campania* v v v v - 
Calabria* v v v v - 
Apulia v v v = 
Central v - 

Adriatic coasts 

Veneto and v v v v 96 
Friuli V.G. 

Sicily* v v v v - 
Sardinia v J 2 000 

Provence Alpes ¥ v v v 3 
Cote d'Azur 


Both below-ground and above-ground biomass values 
of Posidonia oceanica exceed those of other seagrasses, 
including the Australian Posidonia species”. A striking 
feature is the distinct partitioning of the biomass, mainly 
directed into the lignified rhizomes, which can account 
for up to 90 percent of total biomass'*" “and production 
where leaves account for more than 90 percent”. In an 
extensive study net primary production was estimated 
to range from 130-1284 g dry weight/m’/year. However, 

Distribution of seagrasses throughout the western Mediterranean (Italy, France and Spain) 


On rocky and sandy bottom, from 0 to 35 m'”, 

On rocky and sandy bottom, from 0 to 40 m 
Large extensions of dead "matte". Meadows in regression at north of the 


Tevere River due to sedimentation from construction works. Illegal trawling 
within the depth of 40 m7" 

Beds with different typology, extension and morphological features, due to 
the highly variable environmental conditions and sea bottom 

Beds with different typology, extension and morphological features, due to 
the highly variable environmental conditions and sea bottom topography. 
Posidonia oceanica is frequent along the southern Adriatic and the lonian 
coasts. Meadows grow on old “matte” remains, in the Gulf of Taranto, while 
they grow on sand or rocks along the Adriatic side of Apulia. Posidonia 
aceanica is also present at the Tremiti Islands”. 

Posidonia oceanica is absent from the Po River delta to the northern Apulian 
coasts. No information on other seagrasses except for Zostera marina 
(Numana Harbor, south of Ancona). 

Seagrasses are not abundant along the northern coasts of the Adriatic Sea, 
which is influenced by the freshwater inflow and fine sediment coming from 
the Po River. Posidonia oceanica is present only in a few patches in the Gulf 
of Trieste and in the Venice lagoon, where Zostera marina is present in one 
of the few spots of the Mediterranean Sea’ *°”"), 

Posidonia oceanica is present all along the Sicilian coast. Dense prairies are 
present along the southeast and northwest coasts of the island on 
calcareous sediments. Illegal trawling within the 40-m zone has caused 
significant loss of Posidonia oceanica meadows in recent years, together 
with the damage caused by anchoring and recreational activities”, 
Posidonia oceanica extends all along the Sardinian coast, from a few meters 
to 30 m, and occasionally 40 m, depth. Prairies on the southern and northern 
coasts of the island are more fragmented (author's unpublished data). 

Posidonia oceanica is the most abundant species. Cymodocea nodosa: 
dense monospecific meadow from 0 to 15 m depth and mixed beds with 
Zostera noltii and Caulerpa prolifera. Zostera marina: dense meadows 
present in the Gulf of Fos, while small beds occur in the Bay of Toulon. 
Zostera noltii is present in small patches in the Berre lagoon!” *”). 

this production is only minimally used for direct 
consumption by herbivores’. The very high biodiversity 
found in Posidonia oceanica beds is mostly due to the 
primary role of this seagrass as a multidimensional 
habitat for organisms directly participating in the 
system's trophic dynamics‘. 

The Posidonia oceanica matte not only represents 
a net sink of carbon and other elements” “” but also, 
when growing near the surface, can attenuate the wave 
action. Under such conditions, it has been estimated that 

Sites Po Cn Zm Zn Hs Area 
Languedoc- v v v 26 
Corsica v v v 624 
Catalonia v v v v 40 
Valencia v v v 270 
Murcia v v v 95 
Andalucia v v v v - 
Balearic Is* v v v 750 

The western Mediterranean 

the removal of 1 m* of matte can cause 20 m of coastal 


ashore gives rise to a 

. Moreover, the deposition of dead leaves 
typical structure called 

“banquette” which, mixed with sand, can in some areas 


develop up to 2-3 m high 
tant role in attenuation of waves and in the protection 
beaches from erosion’. In addition, the banquette 

. The banquette has an impor- 


hosting a reduced, but highly specialized fauna [isopods, 

amphipods and interstitial flatworms] that contribute 
the decomposition of the seagrass material. 


Posidonia oceanica is present only in small patches between 7 and 15 m 
depth, with dead and living beds 1-4 km from the coast (extent not 
available]. The region is characterized by the presence of many 

coastal lagoons with monospecific Zostera marina beds [e.g. Salse lagoon) 
or mixed beds with Zostera noltii (e.g. Thau lagoons}. In open sea Zostera 
noltii occurs in small patches (e.g. Harbor of Banyuls}"°**” 

Posidonia oceanica meadows on sandy bottom on the east coast and on 
rocky bottom on the west coast. Dense Cymodocea nodosa meadows on 
sand or muddy bottom in shallow bays and in lagoons. Zostera noltil is only 
present in lagoons, often in association with Cymodocea nodosa**:*"". 

Mostly on sandy bottom, but also on rocky bottom. From near the surface 
to 25 m. Conspicuous regressions have been reported, but most meadows 
seem to be stabilized nowadays‘. 

This region has extensive meadows of Posidonia oceanica from near the 
surface to 25 m, exceptionally 30 m, generally on sandy bottom. The deep 
limit has suffered a significant regression due to illegal trawl fishing 
(Sanchez-Lisaso, unpublished data}. 

The main meadows are dominated by Posidonia oceanica, extending from 
the surface to 25-30 m. Conspicuous regressions have been observed near 
the deep limit due to illegal trawl fishing. Cymodocea nodosa and Zostera 
noltii appear in shallow waters'””. 

Posidonia oceanica is abundant in the eastern part of the area, with 
extensive meadows on sandy and rocky substrata. The western limit of 
Posidonia oceanica is near Malaga; from this point westwards (to the 
Gibraltar strait), Zostera marina dominates'””. 

Extensive and dense meadows occur all around these islands, reaching up 
to 40 m depth, with some locally degraded sites, mainly due to tourism 
(moorings, sewage, etc.]. One locality has been invaded by Caulerpa 
taxifolia. In shallow bays, dense Cymodocea nodosa meadows are frequent. 

Cymodocea nodosa is also found below 30 m'””. 

Po Posidonia oceanica; Cn Cymodocea nodosa; Zm Zostera marina; Zn Zostera noltil, Hs Halophila stipulacea. 

/ species present. - insufficient data. 

* Interactions with Caulerpa taxifolia and Caulerpa racemosa. ** 





Case Study 3.3 


The main seagrass species on the Catalan coast is 
Posidonia oceanica. In the sandy coasts of the 
southern part of the country this species forms a 
large and continuous green belt of meadows only 
interrupted by rivers. This seagrass belt used to 
extend from 10 to approximately 25 m depth, 
although significant regressions have been detected 
and in many areas the deep limit is now between 17 
and 20 m. Along the northern rocky coast, the 
meadows occur from near the surface to 20-25 m. 
With the publication of an edict protecting 
seagrasses in 1991, the autonomous government 
(Generalitat de Catalunya) has taken several actions 
for a proper management of these plants and, more 
specifically, of the Posidonia oceanica meadows. 
This includes a monitoring network, launched in 
1998. This network consists of a total of 28 
permanently marked sites [nearly one every 15 km] 
from which basic data on the vitality of Posidonia 
oceanica (e.g. shoot density, cover, etc.] are collected 
every year™!. Underwater work is performed by 

volunteers {more than 400 for the whole project), 

trained and supervised by expert scientists. This 
monitoring network, after the first four years, has 
allowed a general diagnosis of both the status and 
the recent trends of seagrasses on the Catalan 
coast. The results obtained so far indicate that 42 
percent of the studied meadows are in a normal or 
healthy state, while the rest show light (36 percent] 
or strong (22 percent) evidence of degradation. 
During the four-year period of the survey there have 
been no net changes in the Posidonia oceanica beds. 
Only in 15 percent of the sites has a negative, 
although slight, trend been detected from a decrease 
in water transparency, illegal trawl fishing and 
oversedimentation. Overall the Catalan seagrass 
beds appear to have remained remarkably stable 
over the period 1998-2001. 


The Medes Islands are a small and deserted 
archipelago situated 1.6 km off Spain’s main coast, in 
the northern part of Catalonia. A large Posidonia 
oceanica meadow, extending from 5 to 15-20 m 
depth, and covering about 9 ha, is found in the 
sedimentary bottom of the southwest face of the 
main islands. This meadow has been extensively 
studied’ * jn the course of the monitoring program 
of the marine reserve established there in 1990. The 

dataset has one of the longest series for this species, 
and the results show significant interannual 
differences. From the first observations in 1984 and 
1987, density and cover decreased sharply (e.g. at 
the 5 m depth station, density decreased from 628 
+19 shoots/m? in 1984 to 481 +14 shoots/m? in 1994, 
while cover decreased from 76 percent in 1984 to 48 
percent in 1994) probably due, at least in the shallow 
station, to very high mooring activity on the seagrass 
bed. However, after the establishment of the marine 
reserve in 1990 anchoring was no longer allowed, 
and a system of low-impact mooring was deployed 
between 1992 and 1993. The density and cover values 
subsequently recovered [e.g. at the 5 m depth 
station, density reached 708 +24 shoots/m? and cover 
73 percent in 2001). Moreover, it would also seem 
that meteorological conditions [e.g. incoming 
irradiance) in these later years have been optimal, 
probably contributing to the observed increase. 


Although Posidonia oceanica is the most abundant 
seagrass species on the Catalan coast, in some 
specific habitats other marine angiosperms can 
dominate. This is the case in the two bays at each side 
of the Ebro Delta, the southern one of which (Alfacs 
Bay] has been extensively studied and mapped. In this 
bay, 50 km? in extent, dense meadows extend from 
very near the surface to 2-3 m and, more rarely, 4 m 
in depth. This narrow bathymetric range is due to high 
water turbidity. Cymodocea nodosa, with the green 
alga Caulerpa prolifera interspersed in some places, 
dominates these meadows. Some patches of Zostera 
noltii, as well as Ruppia cirrhosa, exist in shallow 
areas. The presence of Zostera marina was detected 
in the early 1980s, but it has never been seen again. A 
detailed map was produced in 1986 revealing a total 
surface of seagrass beds of 3.5 km’, including 1 km? 
of patchy beds in the southern zone. In the last ten 
years, the bay has undergone some remarkable 
vegetation changes”. Cymodocea nodosa has greatly 
expanded in the southern part of the bay, covering 
now about 2.5 km? which represents, for this southern 
area, an increase of approximately 15 percent a year. 
This increase may be associated with work performed 
to stabilize the sandbar, since sand instability was one 
of the main processes controlling seagrass 
abundance in this area®. In the northern parts of 
Alfacs Bay, the most remarkable change is the 
replacement of a mixed Zostera noltii and Ruppia 
cirrhosa bed, described in 1982", by Cymodocea 
nodosa with abundant drifting macroalgae, such as 
Ulva spp. and Chaetomorpha linum, by 1997. 

Mediterranean seagrass meadows host many 
commercially important fish species. As well as 
nurseries they provide essential feeding grounds for 
cephalopods, crustaceans, shellfish and finfish’”. 
Although specific fisheries legislation does not allow 
destructive fishing (e.g. trawling) in seagrasses, such 
restrictions are often violated. The only fishery allowed 
in the Posidonia oceanica meadows are small fisheries 
based on the use of standing nets and cages. 

Posidonia oceanica detritus is used as fertilizer in 
agriculture in Tunisia®” and the leaves have also been 
used in small proportions in chicken feed’, with an in- 
crease in egg production and weight. More recently, 
different attempts to exploit the banquette were focused 
on production of methane’, conversion of detritus into 
fungal biomass'” and formation of dried pellet for prep- 
aration of light bricks for buildings. Further anecdotal 
uses of air-dried leaf detritus to protect glass objects in 
transport, and to fill pillows and mattresses, have been 
reported. Posidonia oceanica detritus is used in Corsica 
as thermal insulation material on roofs’ and as sound- 
proof material”. The ability of Posidonia oceanica leaves 
to produce active substances, which accelerate the 
growth of bacteria such as Staphylococcus aureus, has 
been demonstrated. This seems to be related to the 
Presence of chicoric acid, one of the most abundant 

metabolites found in this seagrass’. 

Beds of Posidonia oceanica have suffered a progressive 
regression throughout the Mediterranean due to 
trawling, fisheries and sand extraction and development 
of coastal infrastructure’’*", such as harbors and 
artificial beaches, and associated enhanced turbidity 
and sedimentation. The damming of rivers has caused 
changes in sedimentation in the littoral zone, either 
exposing or burying seagrass habitats. One dramatic 
example occurred in Port-Man Bay [southeast Spain], 
where a seagrass meadow was buried under a large 
amount of highly toxic mining debris. Eutrophication, 
which decreases water transparency and promotes 
epiphyte overgrowth, is a serious regional threat. 
Sometimes associated with fish cages, the most com- 
mon causes are sewage and industrial waste discharge. 
Caulerpa taxifolia is a tropical green seaweed 
accidentally introduced in the Monaco area in 1984. After 
its introduction, Caulerpa taxifolia spread through 
France, to Italy and Spain (the Balearic Islands) by 1992, 
and to Croatia in 1994". The area colonized has now 
reached more than 60 km’ along the French and Italian 
coasts. Caulerpa taxifolia grows throughout the entire 
depth range of the Mediterranean seagrass species and, 
in some places, is progressively overwhelming them. 
Another strong competitor with seagrass beds is the 
introduced congeneric species Caulerpa racemosa, 

The western Mediterranean 

: Sa a 
Posidonia oceanica growing on rocks and forming matte, Porto 
Conte, Sardinia 

which has become widespread in the last ten years. 
Experimental work on the interactions between intro- 
duced Caulerpa species and local seagrasses show that 
dense meadows of both Posidonia oceanica and 
Cymodocea nodosa are likely to be less affected by 
seaweed invasion. The competitive success of Caulerpa 
racemosa with Posidonia oceanica meadows is a 
function of seagrass density and edge-meadow 
orientation. Competition between Caulerpa racemosa 
and Cymodocea nodosa seems to favor the expansion of 
Zostera noltii**“', The locations of interactions between 
seagrasses and Caulerpa spp. are listed in Table 3.2. 

Although Mediterranean seagrasses are now 
being increasingly well monitored, reliable estimates, 
made by direct observation, of the area of seagrass lost 
or degraded by the various pressures are not available 
for most of the western Mediterranean coastline. In fact 
only in the last few years have maps of distribution 
been produced. In the future the application of aerial 
cartography techniques may supply important 
information on seagrass status throughout the 

In general, for Posidonia oceanica, the following 
statement by the European Union for Coastal 
Conservation is probably accurate: “The situation in the 
Western Mediterranean is serious. Shoot density is 
rapidly decreasing, up to 50 percent over a few decades. 
Besides, increased turbidity and pollution have resulted 
in a squeeze of the beds; in various places living beds 
have withdrawn between 10 and 20 m depth. Dead beds 
occur abundantly, even in waters which have already 
been protected for 35 years. For the French mainland 
coast habitat loss is estimated at 10-15 percent; but 
taking into account the decrease of shoot density the 
overall decline of the resource will be between 30 and 
40 percent. This is probably a good estimate for most 
Western Mediterranean coastlines, although the 

Photo: Laboratory of Benthic Eco 



situation around the islands and in the Eastern 
Mediterranean Is better”. 

In France a disappearance of Posidonia oceanica 
beds between 0 and 20 m has been observed in the last 
30 years for 13 percent of the seafloor in the Alpes 
Maritime department, 6.6 percent in Var and 18.4 
percent in Bouches du Rhéne””*". In Spain, a compari- 
son of old marine charts with present distribution data 
in Catalonia indicates that meadow area is now about 
75 percent of that at the beginning of the 20th century. 


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The western Mediterranean 57 

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Oceanografia 11: 111-119. 

4 The seagrasses of 

The Black, Azov, Caspian and Aral Seas 



Asian seas is their total (Aral and Caspian) or 

near-total [Azov and Black) isolation from open 
ocean systems. These temperate seas have many 
common environmental features especially with regard 
to variable salinity and levels of pollutants. 
Geographical proximity and isolation determine a 
number of special features inherent in these seas: they 
have a distinctly continental climate, no tides (but 
considerable long-term fluctuations of sea level, and 
both coastal upwelling and downwelling, have 
occurred), minimal or zero water exchange with other 
seas and seawater of unusual chemical composition”. 
All four seas contain the estuaries of major rivers and 
are consequently dependent on the influx of freshwater. 
In nearly every case these rivers have been severely 
disrupted from their natural state by the construction of 
dams, and upriver pollution and water extraction, as 
well as changes in rainfall across their watersheds. 
Therefore long-term changes in seawater chemical 
composition and concentration have occurred near the 
river mouths. Distinguishing hydrological charac- 
teristics of the coastal shelves, the main potential 
habitat for seagrasses, are their shallow depth (about 
20 m) and large area, marked seasonal and interannual 
fluctuations in productivity, winter ice cover, pre- 
dominant wind-induced seawater circulation, and fast 
water exchange owing to the small capacity. 

Highest productivity is found in the brackish areas 
of the north Caspian Sea, the northwestern Black Sea, 
and the Sea of Azov and Kerch Strait” “°. This high 
productivity is due to massive freshwater influx from the 
Rivers Volga, Danube and Don, and the correspondingly 
high nutrient input, fast turnover of these nutrients, 
intense summer warming, high dissolved oxygen 
content of the brackish water and the longer summer 
daily growth period at higher latitudes. However, at the 
same time anthropogenic pollution substantially 
reduces the biological diversity and productivity of the 

Ts principal characteristic of the temperate Euro- 

N.A. Milchakova 

water bodies, and has been especially damaging to the 
traditional fisheries of these four seas. In the Caspian 
and Azov Seas, which are of the greatest significance for 
commercial fishing in the region, the usable fish stock 
has been reduced by more than half. The largest 
sturgeon stock in the Caspian Sea has dramatically 
decreased. In the last two years, the commercial stock 
{approximately 250000 metric tons) of  kilka, 
Clupeonella cultriventris, has been reduced by 40 
percent. Twenty thousand Caspian seals and about 10 
million birds have died. High concentrations of heavy 
metals and oil products were detected in the dead 

Seagrasses play a key role in the coastal eco- 
systems of the seas and occupy vast areas in the 
shallow bays and gulfs of the Black, Azov, Caspian and 
Aral Seas. The diversity of algae, invertebrates and 
fishes in seagrass communities is astonishing. The 
condition and distribution of seagrasses are strongly 
influenced by freshwater influx, industrial, municipal 
and agricultural sewage, shipping, sea-bottom 
dredging, dumping, and oil and gas extraction on the 
shelf. Fluctuations in the sea level of the Caspian and 
Aral Seas also influence the coastal ecosystems. 


There are four seagrasses, two seagrass associates 
and about 300 macroalgae in the flora of the Black 
Sea’. Communities of Zostera marina, Zostera noltii, 
Potamogeton pectinatus and Ruppia cirrhosa occupy 
vast areas in shallow bays and gulfs, especially in the 
northwestern part of the sea”. The distribution and 
ecology of Black Sea seagrass was first reported at the 
beginning of the 20th century"" ™, with further details 
of seagrass biology and community structure in the 
Black Sea, and environmental impacts on the 
seagrasses, being obtained in subsequent decades” 
"18! During 1934-37 communities of Zostera marina 
were seriously damaged due to a wasting disease 



Photo: F.T. Short 

RRS Aas 


Early symptoms of wasting disease in Zostera marina - an 
epidemic in the 1930s seriously damaged communities of this 
seagrass in the Black Sea 

epidemic similar to that registered along the North 
Atlantic population of this species'’”. Fortunately, 
Zostera noltii, also widely found in the shallow bays and 
coves, was not affected’ ”., 

During the 1970s and 1980s, the stock of Zostera 
spp. growing in the four largest bays of the Black Sea, 
the Tendrovsky, Dzharilgatsky and Yagorlitsky Bays and 
the Karkinitsky Gulf, was estimated at 633000 metric 
tons’ 7! After 1982 the coasts of these bays 
accumulated considerable cast-off of Zostera spp., 
estimated at 35000 metric tons dry weight’. However, 
according to previously calculated data on the annual 
leaf production of Zostera spp., the actual annual 
estimate was about 4000 metric tons dry weight. 

Many researchers have noted that Zostera spp. 
usually grow in the coastal salt lakes and sometimes in 
the deltas of the rivers'**. There is no information on 
the distribution of Zostera spp. along the shores of 
Georgia and Bulgaria. Zostera noltii is found in Sinop 
Bay, on the Anatolian coast of Turkey. 

Seagrasses in the Black Sea grow in single 
species and mixed communities, located on silt and 
sandy sediments, often with a portion of shell grit. The 
depths at which they are found range from 0.5-17 m, 
across a Salinity gradient of 0.3-19.5 psu. Some 115 
algal species have been identified growing in Zostera 
marina communities, and 62 in communities of Zostera 
nolti!. The majority of the algae are epiphytes 
encrusting the leaves and occasionally the rhizomes 
and roots. Cladophora, Enteromorpha, Ceramium, 
Polysiphonia and Kylinia spp. predominate. There are 
more than 70 species of invertebrates, 34 fishes and 19 
fish larvae in seagrass meadows, among which 
shrimps, scad and perch predominate”. 

The average biomass of Zostera marina in 

Karkinitsky Gulf is 1109 g wet weight/m’ with a density 
of 105 shoots/m?*'”". Lower biomass and higher density 
occur in the Donuzlav Salt Lake (836 g wet weight/m* 
and 218 shoots/m’}"". Near the mouth of the Chernaya 
River, where the salinity is less than in other parts of the 
Black Sea (11-17 psu], seagrass biomass reaches 
2986 g wet weight/m* and density 1136 shoots/m? 7) 
although the maximum biomass values recorded for the 
Black Sea occur in Kamysh Burun Bay in the southern 
part of the Kerch Strait (5056 g wet weight/m’)'"”. In the 
Kerch Strait, which links the Black and Azov Seas, 
Zostera marina biomass ranges from 2008 g wet 
weight/m* at Cape Fonar” to 3958 g wet weight/m? in 
Kerch Bay’, and plant density from 916 to 600 
shoots/m’ respectively. The longest shoots of Zostera 
marina, at more than 2 m, have also been found in the 
Kerch Strait”, though in other areas of the Black Sea 
their length more typically varies between 25 and 100 
cm'*'"!. For Zostera noltii, biomass estimates vary from 
0.5 to 2 kg wet weight/m’; the highest values were 
registered at depths down to 1 m in summer 820.31. 

The total sea-bottom area occupied by Zostera 
spp. in the bays of the northwestern Black Sea is more 
than 950 km’, or 40 percent of the total area of all the 
bays”. Zostera spp. communities cover a similar por- 
tion, about 50 percent, of the sea bottom in shallow bays 
of Sevastopol region, the Kerch Bay and Kerch Strait. 

Though most investigators have acknowledged 
that the recent eutrophication of coastal ecosystems of 
the Black Sea has led to degradation of key benthic and 
plankton communities”, the dynamics of the long- 
term changes observed in Zostera spp. communities 
have revealed that there are many localities, including 
dumping grounds, where recovery of the seagrass beds 
is occurring. Estimates of Zostera marina biomass 
have increased two- to threefold in Laspi, Kazachaya, 
Kamyshovaya, Streletskaya, Severnaya, Holland and 
Kerch Bays, and in the Kerch Strait, over a period from 
1981-83 to 1994-99" '* *7 | The greatest increase in 
biomass, from 1185 to 3958 g wet weight/m’, has 
occurred in Kerch Bay, and the greatest increase in 
shoot density, from 252 to 936 shoots/m’, in 
Streletskaya Bay. This increase in the yield of Zostera 
spp. biomass is probably due to several factors, the 
most significant of which is likely to be reduced 
industrial pollution and the natural resilience of 
Zostera marina and Zostera noltii to environmental 
changes. According to unpublished data obtained by the 
Southern Research Institute for Fishery and 
Oceanography in Kerch, the amount of Zostera spp. in 
meadows in the Karkinitsky Gulf has also increased, 
despite extensive annual excavation of sand. 

My own observations indicate that self- 
restoration and enlargement of Zostera beds Is 
occurring in Sevastopol, Kerch and Yalta Bays, all of 


Sivash National 
Nature Park 
Chemomorsky \ Molochny 
National Reserve \ Salt Lake 
\ | /Belosaraisky 
Yagorlitsky and \ 

Tendrowky Bags ~ Utlyuk \ W, 
: \ sl ate \ 4 ~z, Berdyansky 

{ZO} Fs 

Karkiniishy Gl \ ry — Kerch Srrait 

Danube Delta —* Gulf ‘ 
Biosphere Reserve «= Sevastopol Q4 
3 Lapsi Bay 



Arabaisky Bay 

Donuclay Salt Lake 
Yalta Bay 



3 Sinop Bay 

Q 100 200 300 400 500 Kilometers 

The Black, Azov, Caspian and Aral Seas 

which have been subject to considerable disturbance 
from recreational activities. Indeed not only seagrass 
but all Black Sea benthic macrophytes are stabilizing 
and recovering from recreational pressures over wide 
areas. In contrast seagrass and algae communities are 
most degraded in areas with heavy sedimentation 
loads. This decline has occurred particularly along the 
deepest boundary of macrophyte growth. 

Black Sea Zostera spp. are traditionally used in 
local agriculture as a forage additive and for winter 
insulation for barns for livestock”. It has been proved 
experimentally that the daily yield of milk of cows 
whose fodder was mixed with Zostera marina 
increased by 15-20 percent. Weight increases of 20-30 
percent in sheep fed Zostera, and of 10-15 percent in 
pigs’, have also been observed. Seagrass additives 
appear to increase milk quality and fat in dairy cows 
and provide better quality and quantity of sheep wool. 
Zostera spp. are a valuable source of pectins, aquatic 
solutions which produce firm gels. Being rich in 
hemicellulose and pectin substances, seagrasses are 
also used as a gluing component in mixed fodder 
granulation and packaging. 

In the Black Sea, seagrasses have been placed 
under protection in ten nature reserves under the 
national control of Ukraine and Romania®**. The 
largest of them are the Danube Delta Biosphere 
Reserve and the Chernornorsky National Reserve. 

There are four species of seagrass, three seagrass 
associates and 64 macroalgae in the flora of the sea”. 
The Zostera spp. have a Mediterranean origin and are 
believed to have appeared in the Sea of Azov in the 

The meadows of Zostera noltii are the most 


The Black, Azov, Caspian and Aral Seas 

50° E 6QreE 
Minor Bays and Sea———*, 

Astrakhansky . gsecae 

National Reserve KAZAKHSTAN 




_- Mangyshlaksky Bay UZBEKISTAN 

a ce 




pee Krasnovediky Bay TURKMENISTAN 

AZERBAWAN. © \yoku Buy 



Turkmensky Bay 
Kirova Bay 

extensive and dense compared with other seagrasses. 
This species grows on silt-sandy sediments with shell 
grit from 0.2 to 8 m'“* and across a salinity gradient of 
2-26 psu. Zostera marina inhabits the same depths but 
covers a considerably smaller area. Zostera spp. grow in 
single-species beds and also in mixed communities with 
other seagrasses, mostly Potamogeton pectinatus and 
Ruppia cirrhosa, and with algae such as Ceramium, 
Polysiphonia, Cladophora and Enteromorpha spp. 
Zostera noltii and Zostera marina are found almost 
everywhere along the shoreline of the sea’, and also in 
the coastal salt lakes, river mouths and floodplains. This 
is due to their tolerance to salinity fluctuations. Zostera 
noltii in the Sea of Azov has shoots 15-70 cm long, while 
those of Zostera marina measure 20-90 cm. 

The vast meadows of Zostera noltii and Zostera 
marina predominate in the northern part of the sea, 
close to sandy spits, and in the coastal salt lakes. 
Communities of Zostera noltii are also widely prevalent 
in the eastern Sea of Azov, while Zostera marina is 
found here only in patches”. In the western part of 
the sea, Zostera spp. are rare, being usually found as 
solitary sparse seagrass beds. Along the southern 
coast Zostera spp. are dispersed. Zostera spp., washed 
ashore after the leaf fall, abundantly cover the coast. 
The annual commercial after-storm harvest amounts 
to about 1200 metric tons dry weight. 

Recent field measurements have recorded the 
biomass of both Zostera species around the Sea of 
Azov. Zostera noltii biomass in the bays {wet weights: 
Arabatsky 1197 g/m’, Kasantyp 284 g/m’, Tamansky 
374 g/m’, Belosaraisky 860 g/m’, Obitochny 1180 g/m? 
and Berdyansky 400 g/m’) is generally comparable 
with the salt lakes (wet weights: Sivash 
1157-1 400 g/m’, Molochny 378 g/m? and Utlyuk 667 
g/m’) but higher than the seaward coasts of the large 



oe eee en 

RAS Mae 


sand spits which are such a feature of the Sea of 
Azov (wet weights: Belosaraiskaya 28 g/m’, Fedotov 30 
g/m?, Obitochnaya 45 g/m’ and Berdyanskaya 
30 g/m?)!"® 2839314 The biomass of Zostera marina 
was also measured at three of these locations: in 
Sivash (2000 g wet weight/m’) and Molochny (592 g wet 
weight/m’) salt lakes and Tamansky Bay (219 g wet 
weight/m? at 1 m depth but more than ten times this 
at 3.5 m). 

Analysis of the long-term dynamics of the 
structure of Zostera communities indicates that, 
despite changes in the environment and increased 
eutrophication, the recent 60 years have not been 
marked with radical changes. For example, in the late 
1930s, the biomass of Zostera marina in Utlyuk Salt 
Lake was estimated to range from 213 to 2242 g wet 
weight/m?"' and in the early 1970s from 333 to 1024 g 
wet weight/m?'!. Furthermore, over the past 30 years, 
the biomass of Zostera noltii in Utlyuk Salt Lake has 
increased from 260 to 667 g wet weight/m? |’. 

The local population traditionally uses Zostera 
spp. cast-off to insulate housing, for livestock during 
winter and as an efficient means of deterring rodents in 
barns. The high silica content of this material reduces 
its flammability and therefore its risk as a fire hazard. It 
has been experimentally proved that dried Zostera 
marina mixed with urea is a valuable forage additive for 

Seagrasses of the Sea of Azov have been placed 
under the protection of many international conventions 
and the state laws of Ukraine'!. They are the object of 
protection in seven nature reserves, the largest of 
which are Sivash National Nature Park and the coastal 
Molochny Salt Lake. 


Three species of seagrass, two seagrass associates 
and 65 macroalgae make up the submerged flora of the 
Caspian Sea". The earliest work on the composition 
and distribution of Caspian Sea seagrasses was 
produced in 1784” but it was not until the 1930s that 
the most comprehensive reviews on the topic were 
published“. This was the first time that the 
hypothesis about Zostera noltii 's penetration into the 
Caspian Sea from the Black and Azov Seas was 
advanced. Presumably Zostera noltii was introduced 
from the Mediterranean to the Caspian Sea in the 
Paleocene, 36-65 million years ago. At that time the 
Black Sea, the Sea of Azov and the Caspian Sea were 
connected by the Kumo-Manych Strait. 

Zostera noltii communities were then widely 
distributed throughout the Caspian Sea’**“*“!, typically 
at depths of 2.5-4.5 m along eastern shores, though 
occasionally as shallow as 0.5 m and as deep as 18 m, 
across a narrow range of salinity, 12-13 psu. Single 

species and mixed communities of Zostera noltii were 
found on sand sediments with shell grit but never on a 
silt bottom. Highest productivity takes place in mixed 
communities of Zostera noltii and Charophyceae, 
Ruppia and Potamogeton spp. Species of Chara, 
Ceramium, Polysiphonia, Laurencia, Enteromorpha 
and Cladophora are common algae in seagrass beds. 

The distribution of seagrasses and macrophytes 
in the Caspian Sea changed markedly in the period 
1934-61 to 1967-81. In the 1930s there were extensive 
Zostera noltii beds along western coasts, principally 
Baku and Kirova Bays in present-day Azerbaijan, with 
records indicating the presence of this species at 
Derbent, Izerbesh and Makhachkala, and_ in 
Astrakhansky and Kizlarsky Bays in modern Russia. 
Along the eastern coast Kaidak, Mangyshlaksky, 
Kazakhsy and Turkmensky Bays, and the Mangyshlak 
Peninsula, were the main locations of mixed Zostera, 
Ruppia and Potamogeton beds. Estimates of the 
biomass of Zostera noltii and Ruppia cirrhosa in the 
Caspian Sea at this time were much higher than in the 
present day. In Kaidak Bay, with the salinity of the 
seawater ranging from 25 to 51 psu, the highest salinity 
level ever documented for Zostera noltii, the biomass of 
Zostera noltii was estimated to be 7000-8000 g wet 
weight/m’ and that of Ruppia cirrhosa 10000-12000 g 
wet weight/m? “*. The shoots of Zostera noltii from 
Kaidak Bay were 75-100 cm long, while in the open sea 
the length was 25-30 cm. In comparison with Kaidak 
Bay, in the open sea the biomass of this species was 
substantially less, varying from 100 to 1500 g wet 
weight/m’. The total stock of Zostera nolti for the 
Caspian Sea was estimated at approximately 700000 
metric tons (wet weight), with about 500000 metric 
tons for the eastern and 200000 metric tons for the 
western coast. The area covered by the seagrass in just 
the northeastern Caspian Sea was 1650 km’. 

During the 1950s coastal configurations changed 
and many shallow bays such as Kaidak Bay, in which 
Zostera noltii and other macrophytes formerly 
flourished, vanished and the area of others such as 
Krasnovodsky Bay decreased substantially “““". Ever 
since that time, Zostera noltii communities have been 
degrading, having almost completely vanished along 
the western coast and becoming seriously depleted in 
the east. In 1935-38 the biomass of Zostera noltii along 
the eastern coast ranged from 50 to 8000 g wet 
weight/m?**!. By 1971-74 the range had decreased to 
50-1 300 g wet weight/m?'*“”, and in the early 1980s it 
was 127-1340 g wet weight/m’ ''. Despite the decline 
in biomass the area of some beds in Krasnovodsky Bay 
enlarged considerably, so much so that in the early 
1970s different experts evaluated the stock of Zostera 
noltii in Krasnovodsky Bay to be 200 000-440 000 metric 
tons wet weight. Apparently, such an expansion may be 

due to environmental changes and the drop in sea level 
which brought about the extinction of competing algae 
such as the Charophyceae. 

At present, available data indicate that Zostera 
noltii is only rarely found in the western Caspian Sea at 
Makhachkala and in Kizlarsky Bay. Seagrasses have 
completely disappeared from the southern Caspian 
Sea“ *!. Single and mixed communities of Ruppia 
spp. are found growing in Astrakhansky Bay in the west 
and in Komsomolez, Kazakhsy, Krasnovodsky and 
Turkmensky Bays in the east, on silt sediments at 
depths from 0.5 to 3 m. 

Though the areas of sea bottom covered with 
seagrasses have substantially declined, they are still 
important in the ecology of the Caspian Sea. Seagrasses 
play an important role in the nutrition of invertebrates 
on which the state of commercial fish stocks depends“ 
6.48) In the northern Caspian Sea, Zostera noltii growth is 
of special significance, because this is where wild carp, 
Caspian roach, bream and other valuable fish spawn 
and feed’. Other seagrasses are the usual food item for 
waterfowl. Ruppia spp. constitute up to 25 percent of the 
intestinal content of swans and gray geese and 54-84 
percent of that of ducks. 

The seagrass communities have been placed 
under protection in two national nature reserves 
(Astrakhansky and Krasnovodsky National Reserves). 


There are two seagrasses, Potamogeton pectinatus 
and 16 macroalgae in the flora of the Aral Sea’. 
Presumably Zostera noltii was introduced from the 
Mediterranean to the Aral Sea, also through the Kumo- 
Manych Strait. The most extensive knowledge about 
seagrass distribution had been acquired prior to the 
severe anthropogenic disruption of the Amudarya and 
Syrdarya river systems in the mid-1950s'" that caused 
catastrophic changes to the ecosystem of the Aral Sea 
and adjacent water bodies. 

Zostera noltii grew from 0.1 to 10 m deep, with 
most growth being concentrated at 0.1-2 m depth in 
the northern shallow bays’"’. In the mid-1950s, the 
biomass of Zostera noltii was estimated to be 17 to 
800 g wet weight/m?, with the largest values 
registered near the mouth of the Syrdarya River. In 
recent years, the environmental crisis which Is wiping 
out a large part of the Aral Sea has manifested itself 
in drastic increases in salinity which, in turn, have led 
to changes in the biological components of all 
ecosystems. However, the areas occupied by Zostera 


1 Kosarev AN, Yablonskaya EA [1994]. The Caspian Sea. Backhuys 
Publishers, Hague. 

2 Matishov GG, Denisov W [1999]. Ecosystems and bioresources of 

The Black, Azov, Caspian and Aral Seas 

noltii and estimates of its biomass have increased in 
the northern bays, while in the more brackish area 
near the Syrdarya’s mouth biomass has considerably 
decreased. Records from the early 1990s show that 
biomass is now apparently positively correlated with 
salinity. In the Syrdarya Estuary at salinity of 7 psu 
biomass was just 42 g wet weight/m’, whereas in 
Tshe-Bas Bay Zostera noltii not only tolerates salinity 
as high as 45 psu but thrives on silt-sandy and sandy 
sediments supporting beds with biomass of 2258 g 
wet weight/m’. Intermediate values were observed in 
the Berg Strait (417 g wet weight/m? at 23 psu), 
Butakov Bay (899 g wet weight/m* at 36 psu) and 
Shevchenko Bay (1076 g wet weight/m* at 30 psu)". 
As the Aral Sea continues to disintegrate, Zostera 
noltii communities are expected to persist mostly in 
bays of the Minor Sea, where the sea level has 
remained constant for the past decade. 

Total macrophytic stock in the sea is estimated at 
1.34 million metric tons wet weight. The share 
contributed by Zostera noltii is about 8.1 percent 
(109000 metric tons wet weight}, while algae such as 
Charophyceae and Vaucheria dichotoma contribute 
77.6 and 13.4 percent, respectively'"’. 

Compared to phytoplankton, macrophytes such 
as Zostera noltii are of little importance in the food 
chains of the Aral Sea. However they are ecologically 
important. The meadows of Zostera noltii are the 
spawning location of diverse invertebrates and fish. 
Benthic invertebrates and fish predominantly feed on 
diatoms (Navicula spp. and Merismopedia spp.) and are 
found in abundance”' *’ However, during the past 50 
years, the catches of commercial fish have collapsed to 
the point where the Aral Sea has almost lost its 
significance for fisheries. 

There are no data regarding nature reserves 
along the coastal zones of the Aral Sea. 


| am grateful to Prof. R.C. Phillips (Marine Research Florida Institute], 
0.A. Akimova, G.F. Guseva, M.Yu. Safonov (IBSS), Dr 1.1. Serobaba 
(YugNIRO], Or |.|. Maslov (Nikita Botanical Garden] and Ms Olga 
Klimentova for their help in preparing this chapter. 


Nataliya A. Milchakova, Department of Biotechnologies and 
Phytoresources, Institute of Biology of the Southern Seas, National 
Academy of Sciences of Ukraine, 2 Nakhimov Ave., Sevastopol 99011, 
Crimea, Ukraine. Tel: +38 (0]692 544110. Fax: +38 (0)692 557813. E-mail: 

the European seas of Russia in the late XXth - early XXIst 
centuries. Murmansk. 

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Krasnovodsk Bay. Proceedings of the Institute of Oceanology 23: 

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In: All-Union Conference Marine Algology and Macrophytobenthos. 
VNIRO Publishing House, Moscow. pp 12-14. 

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Black and Caspian seas. Oceanology 7(2): 314-320. 

Salmanov MA [1987]. The Role of Microflora and Phytoplankton in 
Production Processes in the Caspian Sea. Nauka Publishing, Moscow. 
Zaberzhinskaya EB, Shakhbazi ChT [1974]. Bottom Vegetation of 
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Algology and Macrophytobenthos. VNIRO Publishing House, 
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Plants. Kainar Publishing House, Alma-Ata. 

Yablonskaya EA [1964]. About the role of phytoplankton and 
benthos in food chains of organisms inhabiting the Aral Sea. In: 
The Stock of Marine Plants and their Use. Nauka Publishing, 
Moscow. pp 71-91. 

Yablonskaya EA [1960]. The present state of benthos of the Aral 
Sea. Proc VNIRO 43(1]: 115-149. 

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crisis in the Aral Sea”) 250: 21-37 lin Russian). 

The eastern Mediterranean and the Red Sea 

5 The seagrasses of 



his chapter is divided into two sections and 
[cose the seagrasses of the eastern 
Mediterranean and the Red Sea. While the 
eastern Mediterranean has a relatively restricted range 

of species, the Red Sea is home to 11 species, all of 
tropical origin. 


Early contributions from the eastern Mediterranean 
reported on the presence of Cymodocea nodosa [also 
reported as Cymodocea aequorea or Cymodocea 
major}, Posidonia oceanica [also as Zostera oceanica), 
Zostera marina and Zostera noltii {also as Zostera 
nana), in Greece, Syria and Egypt. Halophila stipulacea, 
a migrant from the Red Sea, was first reported in the 
Mediterranean from the island of Rodos late in the 19th 
century". Lipkin’ summarized its distribution in the 
Mediterranean through the early 1970s; during the last 
three decades Halophila stipulacea has spread further, 
mostly in the eastern basin [e.g. Methoni and Paxoi 
Islands, lonian Sea’ *; Marmaris’; Korinthiakos 
Kolpos”*!, but also at and near Sicily" '". 

The most common seagrass in the eastern 
Mediterranean is Cymodocea nodosa. It occurs on all 
coasts of this basin on sandy and, less frequently, 
muddy bottoms. The next most prevalent seems to be 
Posidonia oceanica, a climax seagrass. In many regions 
in the northern part of the basin the balance between 
the two is inverted, with Posidonia oceanica becoming 
the more common. The third in abundance appears to 
be Zostera noltii and the least common Halophila 
stipulacea. Zostera marina, a species common in the 
western Mediterranean, seems to be rare in the 
eastern part, if it still exists there at all. Collections of 
the latter species reported by den Hartog' were from 
the northern parts of the Aegean Sea, made in 1854, 
1891 and 1910. Publications later than 1930, by Greek 
and Turkish authors'"**”, reported Zostera marina from 
the same area. Interestingly, more recent papers about 

Y. Lipkin 
S. Beer 
D. Zakai 

seagrasses on the Turkish and Greek northern Aegean 
coasts" “ do not include Zostera marina among the 
seagrasses of this area. The only report of this 
seagrass from Egypt” - the latter reference being 
based on the former - was probably a case of 
misidentification; in later papers on Egyptian 
Mediterranean seagrasses, Aleem did not mention 
Zostera marina. However, Tackholm et al."" reported 
that the filling of an ancient Egyptian mummy was 
composed of Zostera marina, which indicates that the 
plant must have occurred, or was even common, in 
shallow Egyptian waters some 2000 years ago, and 
seems to have gradually disappeared, first from the 
warmer southeastern corner, then from wider and 
wider areas in the eastern and central parts of the 
eastern Mediterranean, and remained until rather 
recently on its coldest, northernmost coasts. A similar 
retreat from a former, wider range seems also to have 
occurred with Zostera noltii, which is concentrated 
mainly in the Aegean Sea with considerably less 
representation in other parts of the northeastern 
Mediterranean, and almost none in the south. It has 
disappeared, or become very rare, even in the south 
Aegean Sea’. 

Ecosystem description 

Cymodocea nodosa and Zostera noltii usually grow in 
shallow water, from a few centimeters to a depth of 2.5- 
3 m [it has been reported that Cymodocea nodosa 
occupied a depth range of 5-10 m in the Bay of 
Limassol, Cyprus®"]. Posidonia oceanica is found from 
the shallows, where the tips of the leaves reach the 
surface, down to 35-40 m. Halophila stipulacea, many 
beds of which also occur in the shallows, e.g. at Rodos, 
penetrates much deeper water. Bianchi et al.” 
reported it as the deepest seagrass in the Bay of 
Limassol, growing at 25-35 m (for Posidonia oceanica 
they reported a range of 10-30 m). Fresh, seemingly in 
situ, material was dredged from around 145 m off 



Photo: Laboratory of Benthic Ecol 

growing on sand 

Cyprus; however, below about 50 m it was rather 

All four seagrasses grow in the eastern 
Mediterranean on soft bottoms, quartz sand in shallow 
waters and mud at greater depths. Cymodocea nodosa 
frequently occurs in small sandy pockets that 
accumulate in crevices or small depressions on rocky 
flats, and Posidonia oceanica is often found on rough 
substrates such as pebbles and gravel and even solid 
rock. It is noteworthy that Halophila stipulacea, 
growing in a wide range of environmental conditions in 
the northern Red Sea, including all kinds of coastal 
substrates'™“', has a much narrower ecological range in 
the eastern Mediterranean, being restricted in this 
basin to soft substrates only. The form with bullate 
leaves, the so-called “bullata” ecophene, so common in 
extreme conditions in the northern Red Sea, has not 
been reported from the eastern Mediterranean. Several 
ecotypes of Halophila stipulacea occur in the northern 
Red Sea”. Probably only one of them has penetrated 
and spread into the Mediterranean. 

Seagrasses occupy extensive areas in Greek 
waters”. Clusters of Cymodocea nodosa appear in very 
shallow water only a few centimeters deep, mostly in 
sheltered areas, and to a lesser extent on beaches 
exposed to winds and waves. In sheltered areas, 
Cymodocea nodosa tends to occupy deeper bottoms 
and form larger beds. In the southern lonian Sea, such 
beds appear from a depth of 60 cm down to 1.5-2 m. In 
shallower water, the plant is found on sandy bottoms, 
and a little deeper on muddy ones. Posidonia oceanica 

occurs at greater depths, on sandy bottoms. Zostera 
noltii (reported as Zostera nana) was represented by 
scattered plants; no beds are recently reported. 
Halophila stipulacea was rare in lonian Greece around 
1990, occurring at two sites only, at about 2.5 m depth 
at Methoni, together with the siphonous green alga 
Caulerpa prolifera, and at Paxoi*”. 

Most seagrass beds in the eastern Mediterranean 
are composed of one seagrass species only. Beds of 
Posidonia oceanica are usually very dense. Only when 
they start to deteriorate, for example when affected by 
pollution, do other marine plants, usually algae, invade. 
In Cymodocea nodosa beds, the seagrass Is occasionally 
accompanied by Caulerpa prolifera, which may reach 20 
percent of the plant cover’. Mixed populations of 
Posidonia oceanica and Cymodocea nodosa” or Zostera 
noltii and Cymodocea nodosa” also occur. 


Reports on seagrass habitats and community 
structure in the eastern Mediterranean are scanty, 
compared with the information available on these 
subjects in the western basin. The seagrass vegetation 
of the bay at Marsa Matrih Harbor (western end of the 
Mediterranean coast of Egypt) and its close vicinity was 
described by Aleem in the early 1960s". He reported 
healthy beds of Cymodocea nodosa, Halophila 
stipulacea and Posidonia oceanica and provided a 
distribution map. In 1957-60, Cymodocea nodosa beds 
covered a continuous belt 10-40 m wide and about 
750 m long in the inner part of the bay at a depth of 
around 50 cm to 2 m, on the slope between the 
watermark and the horizontal bottom that starts at 2 
m. At the innermost part of the bay, the belt broke into 
scattered patches. In extremely sheltered areas, the 
seagrass was absent. Right below this belt, on the 
lower parts of the slope at 2-8 m depth, a belt of 
Halophila stipulacea of similar size occurred. 
Posidonia oceanica formed a bed 70-120 m wide and 
about 300 m long, outside the inner bay, in an area 
more exposed to winds and waves. 

At El Dab’a, about 160 km west of Al Iskandariya 
(Alexandria), Posidonia oceanica covered a small area 
along with a few small patches of Cymodocea nodosa. 
Halophila stipulacea did not occur at this site. The 
macrofauna and algal macroflora were also scarce, 
both in numbers of species and in numbers of 
individuals. For example, only 12 epiphytic algae were 
found on the leaves and rhizomes of Posidonia 

Aleem! described in detail the establishment, 
development and stabilization of the seagrass beds at 
Al Iskandariya. His description was later incorporated 
by den Hartog'” into his account of the ecology of 
Posidonia oceanica, and therefore will not be repeated 


The eastern Mediterranean and the Red Sea 

Kolpos ~ 

Paxoi ® 

ee _~ lzmir Koérfezi 


/Sikinos vy» Kos 

Methoni ® at 16 = 



Marsa MatrOh x 

El Dab'a 

25° E 

Map 5.1 
The eastern Mediterranean 

here. At that time (the 1950s), however, the Posidonia 
oceanica beds, once established, persisted for long 
periods of time. Later, as in some other Mediterranean 
sites, they became affected by domestic and industrial 
pollution and started to dwindle”. 

The coast of Sinai and the southern part of the 
Israeli coast are mostly covered with pure quartz sand, 
with only a few rocky outcrops here and there. This part 
of the eastern Mediterranean coast, lacking bays and 
coves, Is highly exposed to wind and wave action. Wide 
Cymodocea nodosa beds occur at depths of 2 m and 
more, along the Sinai coast, below the littoral belt in 
which the bottom sediment is intensively worked by the 
breakers. A few small stands of Posidonia oceanica 
were reported by Aleem" from the several rocky 
habitats between Bir Said and El Arish; the status of 
these sites has not been reported since 1955. 

Sabkhet el Bardawil, the large lagoon on the 
Mediterranean coast of Sinai, harbors a large bed of 
Ruppia cirrhosa, which covers up to a third of the 
lagoon’. The size of this bed fluctuates considerably 
seasonally, and during severe winters it may disappear 


Along the generally exposed Israeli coast, rich beds of 
Cymodocea nodosa are found on sandy bottoms at 
sheltered sites. The best developed is at Akko, at the 
northern end of Haifa Bay. Small patches of the 
seagrass also occur in sand-filled depressions on 
submerged horizontal platforms just below mean sea 

Marmaris 320 400 Kilometers 
a | 

Al Iskandariya 


Rodos Island 

Ls Al Ladhiqiyah SYRIA 


Tartods ® —_ Ras Ibn Hani 

Al Arwad 

Satda 6 LEBANON 

Akko @ 

Bur Sa'td 

° Lara 
Sabkhet el Bardawil El 'Arish JORDAN 

Suez Canal 
@ El Suweis 
*®Al' Aqabah (Elat) 

* Sinai 
inal __ Gulf of Aqaba 


— Dahlak 

0 100 200 300 Kilometers ETHIOPIA 

Map 5.2 
The Red Sea 

level. All Cymodocea nodosa populations are subject to 
large seasonal and year-to-year fluctuations in size, on 
occasion disappearing completely, eventually to renew 
from the seed stocks in the sediment’. Area estimates 
for Israel are very approximate since no exact mapping 
has been carried out. We estimate the total Israeli 




Mediterranean coast populations of Cymodocea nodosa 
to be no more than a few hundred square meters. 


From the Lebanese coast there is no information about 
seagrass beds except that gathered by J.H. Powell on 
the occurrence of a Cymodocea nodosa and Halophila 
stipulacea bed some 800 m off Saida (Sidon), in which 
the former comprised 70 percent of the seagrass 
cover. To judge from the very few records of 
seagrasses from the Lebanese coast, seagrass beds 

are uncommon. 


On the Syrian coast, too, seagrass beds are un- 
common". Cymodocea nodosa and Zostera noltii beds 
are found near the river mouths between TartoUs and 
Banias, in the vicinity of Jable, in small, relatively calm 
embayments north of Al Ladhigiyah (Latakia) and near 
the harbors of TartoUs, Al Arwad and Al Ladhigiyah, 
where they grow intermingled with Caulerpa scalpelli- 
formis and/or Caulerpa prolifera’. Zostera noltii 
appears also as an accompanying species in the plant 
community dominated by Caulerpa scalpelliformis at 
Tartods and Al Arwad. 

These seagrasses grow on this coast on clayey 
sand rich in organic matter. They seem to tolerate 
considerable variations in salinity. Posidonia oceanica 
is rare on the Syrian coast; Mayhoub'” found it in only 
two localities: northwest of Al Arwad islet, and in a bay 
near Ras Ibn Hani. In both cases, the beds were not well 
developed; in his opinion they were in the process of 
disappearing. He assumed that the rapid degradation 
of the Posidonia oceanica beds northwest of Al Arwad 
Island, a great part of which were already replaced by 
Caulerpa, was the result of large sewage installations 
that had been constructed a short while previously at 
nearby Tartods“”. 


Seagrass beds are widespread around the island of 
Cyprus. Rich stands of Posidonia oceanica and 
of Cymodocea nodosa are common at different 
depths, Posidonia oceanica beds descending much 
deeper than those of Cymodocea nodosa. Mixed 
populations are found, but less often. Halophila 
stipulacea beds are not as plentiful as those of the 
other two; they also descend to considerable depths”. 
The quickly expanding green alga Caulerpa racemosa 
is considered a threat to the Posidonia oceanica beds. 
Since first noticed in the island in 1991, it has spread, 
unchecked, into a wide range of habitats from the 
shallows to depths of at least 60 m, on sandy as 
well as muddy bottoms, competing directly with 
Posidonia oceanica\“*“*. 


Along the Turkish coasts, at the eastern part of the 
Mediterranean coast, meadows of Posidonia oceanica 
dominate the lower levels of the infralittoral zone, but 
no further information about them is available, except 
that Cymodocea nodosa and Zostera noltii have also 
been found in the area‘. On the Aegean coast, 
monospecific beds of Posidonia oceanica and of 
Cymodocea nodosa were reported from Izmir Bay 
(Izmir Korfezi], as were mixed beds of the two. 
Cymodocea nodosa beds were 20-50 m in diameter, 
whereas those of Posidonia oceanica were much larger 
- 150 m and more in diameter”. Similar meadows are 
probably common on the Aegean Turkish coast. 


From Greek waters, Bianchi and Morri'” reported 
dense monospecific stands of Cymodocea nodosa and 
of Posidonia oceanica at the island of Kos, in the 
eastern Aegean, the latter seagrass appearing to be 
more common. In the western part, large seagrass 
beds were reported from the islands of Sikinos, Milos 
and Pholegandros. Vast beds of Cymodocea nodosa 
were found on mud in shallow bays at the latter two 
localities, at 0.3-4 m depth. Posidonia oceanica was 
common on sandy deposits around the entire coast of 
all three islands studied, not just in bays. In shallower 
water they formed isolated tufts and in deeper water, 2- 
8 m or more, they formed quite large beds". 


Historical and present distribution 

The Red Sea harbors 11 seagrass species, all of 
tropical origin, which penetrated through its relatively 
narrow mouth at Bab al Mandab. These are: Halodule 
uninervis, _Cymodocea_ rotundata, Cymodocea 
serrulata, Syringodium isoetifolium, Thalassodendron 
ciliatum, Enhalus acoroides, Thalassia hemprichii, 
Halophila ovalis, Halophila ovata, Halophila stipulacea 
and Halophila decipiens'* “*. Only a single plant of 
Halophila decipiens has hitherto been reported from 
the Red Sea, grabbed from 30 m™’. For early records 
and distribution see Lipkin". 

Enhalus acoroides seems not to reach much 
beyond the Tropic of Cancer, whereas the other ten 
species continue to the northwestern part of the Red 
Sea proper, but only seven [the above listed species 
excluding Enhalus acoroides, Cymodocea serrulata, 
Halophila ovata and Halophila decipiens) penetrate into 
most of the Gulf of Elat {Gulf of Aqaba) and only five 
(Halodule uninervis, Halophila stipulacea, Halophila 
ovalis, Halophila decipiens and Thalassodendron 
ciliatum) into much of the Gulf of Suez. Hulings and 
Kirkman’ reported Cymodocea serrulata from “a 
shallow lagoon on the west coast of the Gulf of Aqaba 

The eastern Mediterranean and the Red Sea 

40 km south of Eilat”, but this record should be 
confirmed. Halophila stipulacea, Halodule uninervis 
and Halophila ovalis appear at present to be the only 
seagrasses that reach the tips of these gulfs?**°), 
although old records also listed Thalassodendron 
ciliatum and Syringodium isoetifolium from El Suweis 
(Suez), at the tip of the Gulf of Suez, and from Al 
Aqgabah at the tip of the Gulf of Elat, and in addition 
listed Cymodocea rotundata and Cymodocea serrulata 
from El Suweis’". Notably, Aleem'™“! did not find any 
seagrass at Bur Taufiq, near El Suweis. 

Halophila stipulacea, very common in the 
northern part of the Red Sea, is rather scarce at its 
central and southern parts’, as well as at the 
tropical east African coast south of the Horn of Africa. It 
becomes common again on the east African coast near 
the Tropic of Capricorn’. Thus, Lipkin” concluded that 
this species is of subtropical affinity rather than 

Some of the Red Sea seagrasses occur in the 
intertidal zone and most species usually grow at the 
shallow subtidal, not deeper than 5 m, but may be 
found as deep as 10 m'*!. However, Halophila 
stipulacea is widely found in the Gulf of Elat at depths 
down to 50 and even 70 m and Thalassodendron 
ciliatum down to 30 m'*°!. In the Gulf of Suez, 
Halophila decipiens was found at 30 m, Halophila ovata 
down to 20 m and one of the populations of Halophila 
ovalis at 23 m'™”’. On the Jordanian coast of the Gulf of 
Elat, two Halophila ovalis stands were found at 15 and 
28 m, respectively”. 

Most seagrasses in the Red Sea grow on mud, silt 
or fine coralligenous sand, or mixtures of them. The 
eurybiontic Halophila stipulacea and, to a lesser extent, 
Halodule uninervis thrive on a wide variety of 
substrates. Thalassodendron ciliatum and Thalassia 
hemprichii, however, seem to prefer coarser substrata, 
that is coarse sand admixed with coral and shell debris 
or even rather large pieces of coral from the 
surrounding fringing reefs or coral knolls at sites 
exposed to considerable water movement”. 

Almost all beds of Thalassodendron ciliatum and 
Enhalus acoroides are monospecific, whereas 
Syringodium isoetifolium, Thalassia hemprichii and 
Halodule uninervis often occur in multispecific 
seagrass communities. This tendency also changes 
geographically, e.g. Syringodium isoetifolium forms 
monospecific stands as well as occurring in 
multispecific communities on the central Saudi Arabian 
coast, whereas in the Gulf of Elat it was found only in 
mixed populations. 

Although seagrass beds are common in the Red 
Sea, information about the seagrass habitats and plant 
communities in this basin is very limited. A general 
account of Red Sea seagrass beds was given by 

The northern Red Sea taken from the Space Shuttle. The Red Sea 
harbors 11 seagrass species - all of tropical origin. 

Lipkin’, including information about the typical 
accompanying fauna. Below is a summary of the few 
available descriptions of the seagrass vegetation in 
some Red Sea localities. 


In the south, within the Dahlak Archipelago, on the 
Eritrean coast, seagrasses are not common. A sparsely 
vegetated Caulerpa racemosa-Thalassia hemprichii 
community was reported from sandy patches at the 
lowermost intertidal zone’. Small patches of 
Halophila stipulacea and Halophila ovalis were also 

found in the archipelago”. 

Saudi Arabia 

For the central part of the Saudi Arabian coast, in the 
Jeddah area, Aleem'“” reported in the late 1970s that 
Thalassodendron ciliatum, Syringodium isoetifolium, 
Enhalus acoroides, Halophila ovalis and Halophila 
stipulacea grew predominantly as pure stands, but 
were sometimes mixed with other seagrasses. He 
remarked that Thalassia hemprichii, Cymodocea 
rotundata and Halodule uninervis tended to form mixed 
communities. Thalassodendron ciliatum beds, to 20- 
30 m’ in size, grew on coarse coralligenous sand with 
shell debris and sometimes on dead corals that were 
covered by a thin layer of sand. These stands of the 
seagrass appeared at about 2 m or a little deeper’. 
Beds of Thalassia hemprichii, to 100 m? in size, were 

NASA archive number ST040-78-88, 1991 





plentiful on the central coast of Saudi Arabia; they 
appeared at 1-2 m depth as mixed vegetation in which 
Thalassia hemprichii constituted 60-70 percent of the 
plant cover, Cymodocea rotundata 20-30 percent and 
Halodule uninervis 10-20 percent. Pure stands of 
Halodule uninervis were common on this coast in 
shallow water. In very shallow lagoons, a thin-leaved 
form appears, whereas on open coasts, a little deeper, 
the beds are composed of the wide-leaved form. 
Cymodocea serrulata dominates in seagrass beds 
between 0.5-2 m deep, making up 70 percent of the 
plant cover. In the shallower beds [0.5-1 ml, it is 
accompanied by Halodule uninervis and Halophila 
ovalis and in the deeper beds (1-2 m] by Cymodocea 
rotundata and Halodule uninervis. Small, 0.5-4 m? in 
size, almost pure patches of Syringodium isoetifolium 
occurred at one site along this coast at depths 
of 0.5-1m. The green alga Caulerpa serrulata 
accompanied the dominant seagrass in these patches. 
In another site, Syringodium isoetifolium was mixed 
with Thalassia hemprichii, Cymodocea rotundata and 
Halodule uninervis. Beds of Enhalus acoroides were 
unusual on the central Saudi Arabian Red Sea coast. 
Pure patches, about 30 m’ in size, grew at 1-2 m on 
coarse sand with shell debris on top and black mud 
below, in one site on this coast. Halophila ovalis formed 
small patches, 0.5-2 m in diameter, of sparse growth in 
shallow water in most localities visited”. 

Gulfs of Suez and Elat 
At the Gulf of Suez and the Gulf of Elat, in the north, 
thin-leaved Halodule uninervis formed sparse 

Case Study 5.1 

Along the Israeli coast of the Gulf of Elat, at the 
northwestern end of the gulf, Halophila stipulacea 
is the only seagrass found at all sites but one (the 
middle of the site south of the Marine Laboratory, 
where a small bed of Halodule uninervis is also 
present}. In 2001 the distribution of Halophila 
stipulacea was follows: 

Along the northern shore of the Gulf of Elat. 
An extensive bed of Halophila stipulacea 
occurs along the northern shore of the Gulf 
of Elat, probably extending towards and 
beyond the nearby Jordanian town of Al 
Agabah. The plants grow at depths from 5 m 
to more than 45 m, with the highest densities 

monospecific prairies in the lower intertidal zone of 
muddy coasts. In the subtidal zone, pure stands of this 
seagrass were much denser, and the plants were 
larger. Mixed stands of Halodule uninervis with 
Halophila stipulacea, and sometimes also Halophila 
ovalis, were common in the two gulfs as well °°. Four 
other communities dominated by Halodule uninervis 
were reported from the Sinai coast of the Gulf of Elat: 
the Halodule uninervis-Syringodium isoetifolium 
community, the Halodule uninervis-Syringodium 
isoetifolium-Halophila stipulacea community, the 
Halodule uninervis-Cymodocea rotundata community 
and the Halodule uninervis-Halophila  ovalis 
community. Vegetation types dominated by Halophila 
stipulacea occupy a wide range of habitats. Mostly 
Halophila stipulacea is represented by rather dense 
monospecific beds that extend between the lower 
intertidal zone and depths of 50-70 m at the Gulf 
of Elat. 

Density in these beds decreases below 10 m'". 
Here and there mixed stands occur, in which Halophila 
stipulacea is accompanied by Halodule uninervis or 
Halophila ovalis, and in one small patch near Zeit Bay 
(Ghubbel ez-Zeit) at the mouth of the Gulf of Suez, also 
with Thalassodendron ciliatum*. The Thalasso- 
dendron ciliatum community is the most complex of 
Red Sea seagrass communities, and probably the most 
important for other life forms. The roomy space under 
the seagrass canopy and between its woody vertical 
stems harbors larvae of many pelagic animals, as well 
as its own assemblage of sciaphilic plants and animals. 
The height of these vertical stems, varying with depth 

{and the largest-leaved shoots) occurring 
from 18 to 25 m. The extent of the bed, as 
well as biomass within the bed, has been 
observed to fluctuate during the last few 
years, with a general decline during the last 
Six years. 

Several sites are located near the navy base 
and the commercial harbor. Plants grow at 
depths from 8 to more than 25 m. 

A further site is near the harbor where oil 
and petrol are unloaded. Plants grow at 20- 
30 m depth. 

A substantial site extends from just south of 
the Steinitz [Interuniversity] Marine 
Laboratory to the Egyptian border. Plants 
grow at depths from 7 m to over 30 m. 
Between this and the site near the harbor, 
there are sporadically occurring smaller 
(<100 m*) beds. 

The eastern Mediterranean and the Red Sea 

from around 15-20 cm at the shallows to more than 1m 
at 30 m depth, determines the volume of this under- 
canopy space. 

Thalassodendron ciliatum is unique among Red 
Sea seagrass communities in extending right up to 
coral reefs, without the usual “halo” zone that typically 
separates reefs from seagrass beds in their proximity. 
This halo is formed by reef fishes grazing on the other 
seagrasses. Standing stock of the Thalassodendron 
ciliatum community is by far the highest among Red 
Sea seagrass communities; its productivity, however, is 
among the lowest. This seeming contradiction stems 
from the extremely low consumption of most of the 
organic matter produced by the seagrass and by 
epiphytic algae in the under-canopy space. The only 
highly productive and quickly consumed element in this 
community is that of photophilic epiphytic algae of the 
upper, well-illuminated surface of the canopy, on which 
many herbivorous fishes and invertebrates, mainly 
snails, graze °°"), 

The Syringodium isoetifolium community is rare 
in the Gulf of Elat, where it forms small patches. 
However, the plant accompanies other seagrasses in 
communities they dominate. Monospecific stands of 
sparse vegetation of Halophila ovalis usually appear in 
the Gulf of Elat as a narrow belt at the lee margins of 
larger stands of Halophila stipulacea, or in clearings 
within wide beds of the latter. Mixed stands of Halophila 
ovalis, Halophila stipulacea and Halodule uninervis 
appear in wider areas. Cymodocea rotundata beds are 
the second least common seagrass community in the 
Gulf of Elat, forming monospecific dense stands down 
to 2m. 

Thalassia hemprichii, although the least common 
seagrass on the Sinai coast of the Gulf of Elat, 
dominates in four communities at the southern part of 
this coast. The first is represented by dense mono- 
specific beds growing ona layer, about 30 cm thick, of 
very coarse-grained substrate made of gravel-sized 
coral debris covering the underlying rock. Beds of 
Thalassia hemprichii and Halophila stipulacea in equal 
proportions occurred on the same type of substrata, 
but the unconsolidated layer was somewhat thicker. 
Wide areas of Thalassia hemprichii with Thalasso- 
dendron ciliatum appeared at Ras Muhammad, on the 
tip of the Sinai Peninsula, to the seaward of mono- 
specific Thalassia hemprichii stands on a thin 20-cm 
layer of even coarser unconsolidated material. Finally, 
large areas of dense vegetation of Thalassia 
hemprichii, with 20-40 percent Halodule uninervis, 
covered large stretches of wide reef flats between 
Marsa abu Zabad and Shorat el Mangata’, growing on 
coarse coralligenous sand at 0-30 cm below the low 
water of spring tides". 

The total populations of Halophila stipulacea on 

Sea, Jordan 

the Israeli Red Sea coast [only about 5 km long) 
probably occupy some 0.5-1.0 km’. 


Most of the few reports on pollution effects on seagrass 
beds in the eastern Mediterranean and the Red Sea 
refer to chemical pollution. Haritonidis et al.” in 1990 
reported considerable declines in the sizes of beds of 
Posidonia oceanica and Cymodocea nodosa in the 
Thermaikos Kolpos (northern Aegean Sea) during the 
preceding two decades, with the former suffering 
greatest losses. They also remarked that the density of 
the shoots had decreased, and that marked changes in 
the seagrass epiphytic communities had taken place. 
The authors attributed these phenomena to the 
increased amounts of domestic and _ industrial 
pollutants discharged into the gulf during that period. 
In contrast, Zostera noltii, the least common of the 
three seagrasses that occur in the gulf, seemed to have 
benefited from the increased discharge of sewage, as 
the area covered by its beds had increased. 

A similar decline in the area occupied by 
Posidonia oceanica beds, and their thinning, was 
reported for Cyprus‘, but here the authors attributed 
these phenomena to competition with the invading 
green alga Caulerpa racemosa. Between 1992 and 
1997, dense stands of the latter replaced Posidonia 
oceanica in part of the area it had covered at the 
beginning of this period [total plant cover in the 
Posidonia oceanica beds decreased from 70-90 
percent to 40-60 percent), and a number of algae, not 
previously found in the thinned beds, penetrated into 
them, not replacing Caulerpa prolifera, an accom- 
panying species in some of the Posidonia oceanica 
beds during the earlier period. Similarly, Fishelson et 
al." reported that Halophila stipulacea meadows, 

Photo: M. Kochzius 




formerly widespread, dramatically retreated at the 
northern end of the Gulf of Elat, in the northern Red 
Sea. Here the source of pollution was fish culture in 
cages in the gulf. 

Dando et al.” dealt with the effects of thermal 
pollution. They reported that Cymodocea nodosa 
replaced Posidonia oceanica near hydrothermal 
discharge vents at the bottom of the Aegean Sea. 


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Aleem AA [1980]. Contribution to the study of the marine algae of 
the Red Sea. IV - The algae and seagrasses inhabiting the Suez 
Canal (systematic part.) Bulletin of the Faculty of Science, King 
Abdul Aziz University, Jeddah 4: 31-89. 

Lipkin Y [1991]. Life in the littoral of the Red Sea (with remarks on 
the Gulf of Aden). In: Mathieson AC, Nienhuis PH leds] Intertidal 
and Littoral Ecosystems of the World. Ecosystems of the World. Vol 
24. Elsevier, Amsterdam. pp. 391-427. 

Pichon M [1974]. Dynamics of benthic communities in the coral 
reefs of Tulear [Madagascar]: Succession and transformation of the 
biotopes through reef tract evolution. Proceedings of 2nd 
International Coral Reef Symposium 2: 55-68. 

Lipkin Y [1987a]. Seagrasses of the Sinai coast. In: Gvirtzman G, 
Shmueli A, Gardus Y, Beit-Arieh |, Har-El M (eds) Sinai, Pt 1: Sinai 
- physical geography. Eretz, Ministry of Defence Publishing House, 
Israel. pp 495-504 (in Hebrew). 

Lipkin Y [1987b]. Marine vegetation of the Museri and Entedebir 
Islands (Dahlak Archipelago, Red Seal. Israel Journal of Botany 36: 

Lipkin Y, Silva PC [in press]. Marine algae and seagrasses of the 
Dahlak Archipelago, southern Red Sea. Nova Hedwigia. 

Lipkin Y [1988]. Thalassodendron ciliate in Sinai (northern Red Sea] 
with special reference to quantitative aspects. Aquatic Botany 31: 

Fishelson L, Bresler V, Abelson A, Stone |, Gefen E, Rosenfeld M, 
Mohady 0 [2002]. The two sides of man-induced changes in littoral 
marine communities; eastern Mediterranean and the Red Sea as 
an example. The Science of the Total Environment | in press} online 
uncorrected proof. 

Dando PR, Stuben D, Varnavas SP [1999]. Hydrothermalism in the 
Mediterranean Sea. Progress in Oceanology 44: 333-367. 




6 The seagrasses of 



(hereafter called “the Gulf") is a unique biotope. 

The Gulf is a shallow semi-enclosed sea 
measuring ca 1000 km by 200-300 km''*. The average 
depth is only 35 m. The maximum depth of 100 m 
occurs near the entrance to the Strait of Hormuz. There 
are vast areas in some of the Gulf States, such as the 
United Arab Emirates (UAE), Saudi Arabia and Bahrain, 
with shallow areas less than 15 m deep suitable for 
seagrass growth. 

Seagrass habitats have been designated a critical 
marine resource in the Gulf”. They have also been 
listed as a key renewable resource” “|. 

There are only three species of seagrass in the 
Gulf. It is considered to be a very stressful habitat for 
seagrasses", characterized by large seasonal air and 
water temperature variations, fluctuating nutrient 
levels and high salinities. The three species found are 
considered to be tolerant of such conditions (Table 6.1). 
Outside the Gulf, as many as 11 seagrass species have 
been described for the Red Sea area’. Seven species 
are known in the Arabian Sea” '”'“, seven species in the 
Gulf of Aqaba’ "*'' and eight in the Gulf of Suez”. 

Jones’ observed that seagrasses occur at only 
six locations in Iran. He stated that the Iranian coastline 
was mainly rocky. No seagrasses have been reported 
for Iraq. Seagrass occurrence in Kuwait is quite 
sparse’. Jones’ stated that Halodule uninervis was 
the principal species in Kuwait and reported that large 
beds of seagrasses extended along the coasts of Saudi 
Arabia. However, IUCN-The World Conservation 
Union"! diagrammed seagrasses along the entire Gulf 
coastline occurring in scattered locations. As a whole, 
the resulting report stated that seagrasses were of only 
limited occurrence along the Saudi Arabian coast. 
Price'’” sampled at 53 sites along the entire coastline 
and found seagrasses at only 15 sites. The largest beds 
of seagrass occurred in the north between Safaniyah 

Ts seagrass ecosystem of the Arabian Gulf 

R.C. Phillips 

and Manifah, in Al-Musallamiyah, south of Abu’Ali, in 
Tarut Bay", in the Dawhat Zalum (Halfmoon Bay), parts 
of Al Ugayr and in the Gulf of Salwah'’. Seagrass 
occurrence around Bahrain is extensive”. Sheppard et 
al." stated that seagrasses were extensive along the 
coasts of Qatar, but failed to provide documentation or 
maps. The seagrass occurrence in the UAE is also 
extensive'”. An estimated seagrass occurrence of 5500 
km? occurs in Abu Dhabi Emirate alone. 

Jones" stated that while the coastline of Iran was 
mainly rocky, the western and southern coastlines of 
the Gulf were soft sediments. It also appears that the 
Gulf has its most extensive shallow flats on the western 
and southern coastlines. From an analysis of the 
largest seagrass beds within the Gulf, the beds 
increase in size as one proceeds eastward along the 
southern shoreline. 


The Arabian Gulf is characterized by large seasonal 
temperature variations. The area is arid and very hot for 
many months of the year. There are few rivers that 
drain into the Gulf. There is little rainfall and very little 
freshwater runoff. In addition, the evaporation from 
Gulf waters leads to salinities averaging 40 psu, but 
which exceed 70 psu in the Gulf of Salwah"'. Price and 
Coles'”” reported that inshore waters of the Gulf vary 
seasonally in temperature from 10°C to 39°C and 
offshore from 19°C to 33°C, with salinities varying from 
38 psu to 70 psu. The three species which are found in 
the Gulf can tolerate these extreme conditions: 
Halodule uninervis, Halophila ovalis and Halophila 

Very few studies on seagrasses in the Gulf have 
been produced reporting density, biomass and primary 
production values. Basson et al.” calculated the aver- 
age dry weight of seagrass leaves in Tarut Bay (Saudi 
Arabia) to be 128 g/m’. They doubled this value for an 

annual average. They calculated the energy content of 
the 175-km‘’ seagrass bed in the bay to be 1.4 x 10"' kcal, 
an energy equivalent of about 95000 barrels of oil. 

Price and Coles'’' took samples from a series of 
sites along the entire Gulf coast of Saudi Arabia. They 
took triplicate samples at eight stations during four 
seasons in 1985 and three seasons in 1986. Seagrass 
biomass values ranged from 6.0 to 435 g dry weight/m’ 
(means for each station ranged from 53.3 to 234.8 
g/m’). They reported significant correlations between 
seagrass biomass and depth, sediment hydrocarbons 
and sediment grain size, but no significant correlations 
between biomass and season, salinity, or nutrient 
concentrations and heavy metals. 

Kenworthy et al.'" reported total biomass of 
Halodule uninervis from two heavily oiled sites at Ad 
Dafi and Al-Musallamiyah (northern Saudi Arabia), 
ranging from 50 to 116 g dry weight/m’. At one non- 

Table 6.1 
Seagrass species in the Arabian region 

Arabian Gulf © Number of species 
Iran i 
Iraq 0 
Kuwait 2 


Halodule uninervis 
No seagrass 
Halodule uninervis 
Halophila ovalis 
Halodule uninervis 
Halophila ovalis 
Halophila stipulacea 
Halodule uninervis 
Halophila ovalis 
Halophila stipulacea 
Halodule uninervis 
Halophila ovalis 
Halophila stipulacea 
Halodule uninervis 
Halophila ovalis 
Halophila stipulacea 

Saudi Arabia 


United Arab 

ArabianSea Number of species 
Oman 4 


Halodule uninervis 
Halophila ovalis 
Syringodium isoetifolium 
Thalassodendron ciliatum 
Cymodocea serrulata 
Enhalus acoroides 
Halodule uninervis 
Halophila ovalis 
Syringodium isoetifolium 
Thalassia hemprichii 
Thalassodendron ciliatum 

The Arabian Gulf and Arabian region 

2 ‘ 
4. Karant CULR 
Manifah—_%s Jana | 
At-Musallamiyah—“@go Turi Buy ~~ 

Ad Daf / & BAHRAIN 
ba S Hawar Is 

Jubail Marine _— 
Wildlife Sanctuary Strait of 
© lore 

A Aaziyah 4)” QATAR 

Al Ugayr ~~ Abu Dhabi* » ,, 

‘asht Adhm UAE 
Gulf of Salwah 


0 100 200 300 400 500 Kilometers 

Map 6.1 
The Arabian Gulf and Arabian region 

oiled outer bay site nearby, the biomass was 188 g dry 
weight/m*. For Halophila ovalis, the lowest values were 
observed in the oiled inner bay stations (12 and 17 g dry 
weight/m‘], while the largest biomass was found in the 
non-oiled outer bay site (39 g dry weight/m’}. The 
biomass of Halophila ovalis was nearly three times 
greater at another heavily oiled site (Jinnah Island) as 
compared to an unoiled site (Tanequib) (34 compared 
with 12 g dry weight/m’). Densities of Halodule 
uninervis varied from a high of 5879 shoots/m’ at oiled 
inner bay and mid-bay stations at Dawhat Al- 
Musallamiyah to the lowest densities recorded for oiled 
inner bay and mid-bay sites at Dawhat Ad Dafi (1960 to 
3250 shoots/m’). Densities for Halophila ovalis at 
heavily oiled inner and mid-bay sites at Dawhat Al- 
Musallamiyah and Dawhat Ad Dafi ranged between 
1530 and 2533 leaf pairs/m’. A similar range of values 
existed for Halophila stipulacea. At oiled sites at 
Tanequib and Jinnah Island, densities ranged from 
1721 to 3776 leaf pairs/m* for Halophila ovalis, with a 
single value of 2772 leaf pairs/m* for Halophila 
stipulacea at Tanequib. This study was conducted in 
1991, one year after the Gulf War oil spill. 

In Tarut Bay, Basson et al.” derived tentative 
productivity values by converting from biomass values 
of seagrass leaves. They estimated the production 




value of the leaves to be 100 g carbon/m*/year. These 
calculations did not include the productivity of roots and 
rhizomes. These values included many assumptions 
and were largely hypothetical”. 

Kenworthy et al. determined the net leaf 

Case Study 6.1 

In the summer of 1982, civil engineers won a 
contract to build a roadway from Saudi Arabia 
across 25 km of sea to the island state of 
Bahrain””. The causeway, consisting of five bridges 
linked by seven solid embankments, carries two 
parallel roads from Jasrah on the northeast coast 
of Bahrain, across Umm Na’san Island, over the 
Gulf of Bahrain to join the Saudi coastline at Al 
Aziziyah. The largest of the bridges weighs 1200 
metric tons, and passes 28.5 m above the water. It 
can carry 3000 vehicles per hour. Halfway between 
Umm Na’san and Al Aziziyah, an artificial island 
was built to house coastguards, customs and 
immigration offices. Madany et al.*"' stated that the 
total cost of the project was US$564 million, and 
was one of the largest projects undertaken in the 
Middle East during the 1980s. 

At least half of the causeway’s span consists 
of embankments of dredged rocks and fine mud 
spoil. In consideration of the massive negative 
impacts which this project could have on the 
extensive seagrass beds of Bahrain, the Regional 
Organization for the Protection of the Marine 
Environment from Pollution (ROPME) arranged to 
cooperate with Bahrain's Directorate of 
Environmental Affairs to carry out an ecological 
study on the possible effects of building the 
causeway. A team from the Tropical Marine 
Research Unit at the University of York carried out 
the study through IUCN and the United Nations 
Environment Programme (UNEP]. 


Sampling was done in three visits in 1983, each of 
about one month. Flora and fauna, and 
temperature, salinity, turbidity and chlorophyll 
concentrations, and zooplankton were sampled at 
six coastal and six offshore sites. 

Many of the sites sampled were deemed to 
be critical habitats. In the immediate vicinity of the 
causeway between Umm Na’san and the main 
island of Bahrain, the water was found to be 9 psu 
more saline in the now partly enclosed bay on the 
south side of the road than just to the north, less 

productivity of Halodule uninervis at a single oiled 
station at Dawhat Ad Dafi. Values ranged from 0.094 to 
0.250 g dry weight/m*/year. 

Durako et al." exposed plants of all three species 
from a well-flushed area seaward of the south of 

than 100 m away. Of greater concern were the 
more obvious physical impacts of dredging and 
reclamation. The water became more turbid the 
closer the team moved to the construction work. 
Long plumes of sediment stretched downstream 
from the construction areas. Just to the north of 
the causeway, it found a layer of very fine silt mud 
20 cm thick, with a complete absence of surface 
flora and fauna, but a high abundance of infaunal 
polychaete worms dominated by Ceratonereis. 
Below the silt was a once healthy bed of seagrass, 
now almost completely dead. This was probably 
once a part of a large nursery of shrimp within the 
bay area, as large numbers of juveniles and fish 
thrived in the nearby intertidal flats. These flats 
also supported a rich fauna, including crabs and 
mollusks. At two sites south of the causeway on 
the west coast of Bahrain there was no clear 
evidence of damage. 


At the offshore sites on the east coast, where 
relatively unspoiled conditions were expected, the 
team instead found turbid water. On calm days, 
visibility was only 60 cm into the water, and a layer 
of fine silt covered the seabed out to the coral 
reefs. These reefs were already displaying the 
classic symptoms of sedimentary stress, with 
horizontal faces showing bleached skeletons 
devoid of polyps. The round heads of Platygyra 
looked like a monk's head with a tonsured haircut, 
with the top bleached white. Dead and dying 
branches of Acropora were covered with sea 
urchins or were turned green by colonies of 
epiphytic algae. 

Madany et al." did not state whether this 
project was regulated by the Environmental 
Protection Committee of Bahrain. This committee 
has established specific rules and regulations to 
control dredging and reclamation projects before 
implementation. However, the authors found that 
some projects were carried out without the 
permission of the committee, due to the lack of 
legislation to support the regulations. 

Dawhat Al-Musallamiyah, Saudi Arabia, to un- 
weathered Kuwait crude oil. The treatment duration 
was 12 to 18 hours. There were no significant 
photosynthesis as against irradiance response effects, 
nor were there any effects noted on respiration rates. 
Their conclusion was that the Gulf War oil spill 
primarily impacted intertidal communities, rather than 
the submerged plant communities of the northern Gulf 

Phillips et al." found density values of Halodule 
uninervis from five sites in the UAE to vary from 1745 to 
21590 shoots/m’, while leaf pair densities of Halophila 
ovalis from two sites varied from 166 to 1108/m’. 

Outside the Gulf, Wahbeh’” and Jones et al." 
using oxygen release methods, estimated values of 
1326 g carbon/m’/year for Halodule uninervis in the 
Gulf of Aqaba, 617 g carbon/m*/year for Halophila 
stipulacea and 11 g carbon/m*/year for Halophila 

The studies of Basson et al.’ and Price et al.’ 
suggested that primary production from seagrass and 
shallow water benthic algae may be of greater 
importance in the Gulf than that from phytoplankton. 

Coles and McCain’ identified a total of 834 
species associated with seagrass and sand/silt 
substrates at seagrass stations north of Al Aziziyah 
(Saudi Arabia). Mean numbers of benthic organisms in 
the seagrass beds averaged nearly 52000/m’, an 
average of 36000/m’ in the Manifah-Safaniyah area” 
and up to around 67000/m* in Tarut Bay. 

Basson et al.’ reported a total of 530 floral and 

Case Study 6.2 

Price” devised a simple, rapid assessment 
technique for coastal zone management 
requirements. The method was based on semi- 
quantitative [ranked] data on coastal resources, 
uses and environmental impacts. He recorded 
data at 53 geographically discrete sites, at 
intervals of usually less than 10 km along virtually 
the entire 450-km Saudi Arabian Gulf shoreline. 
Each sampled site comprised a quadrat 500 m x 
500 m, bisecting the beach. Within each quadrat, 
the abundance or magnitude of the mangroves, 
seagrasses, halophytes, algae and freshwater 
vegetation were estimated and recorded semi- 
quantitatively. The attributes were scored using a 
ranked scale of 0-6 {0 was no impact; 6 was the 
greatest impact]. For the resources, abundance 
scores were based on estimates of areal extent 
(m?) for flora, or of estimated number of 

The Arabian Gulf and Arabian region 

faunal species associated with the seagrass beds in 
Tarut Bay, an area of 410 km’. McCain! found 369 
species of benthic organisms in the seagrass beds on 
the Saudi Arabian coast between Manifah and Bandar 

The major associated animal species of the 
seagrass beds of the Gulf are dugongs, green sea 
turtles, pearl oysters and shrimp" * °°". Jones" 
stated that the collapse of the shrimp fishery in the 
northern Gulf has been largely attributed to the loss of 
the critical seagrass habitat. 

The preliminary studies done by Basson et al."” 
suggested that the annual production of the Tarut Bay 
seagrass beds may be about 230 million kg wet weight 
per year. This, in turn, might be expected to yield 2.3 
million kg of fish, at a value of US$8 million annually, or 
the same quantity of shrimps at a value of US$12 
million per year {conversion rate of 1 percent efficiency 
for use of seagrass for fish and shrimps). 

IUCN estimated that the industrial shrimp 
fishery in the Saudi Arabian Gulf and the Red Sea 
totaled some 6800 metric tons, with a value of 
US$35.28 million. The net profit was US$13.94 million, 
an increase of US$4.78 million from 1982. The IUCN 
report concluded that this economic value of the Saudi 
Arabian fisheries would be maintained and increased, 
but only if managed on a sustainable basis. It also noted 
that shrimp production had dropped over the five years 
previous to the date of the report. This was the result of 
either the resource being overexploited, or a 
destruction of the critical seagrass habitat, or both. 

individuals for fauna, both within each sample 
area of the quadrat. Cluster analysis was applied 
after the scores were recorded. The method 
chosen for analyzing the biological resource data 
and the resource uses/impacts was the Bray- 
Curtis similarity index, followed by a hierarchical 
clustering of sites, using the arithmetically 
determined centroid. The results of the cluster 
analyses were depicted as dendrograms. 

Correlations were determined between, and 
within, the following groups of variables: biological 
resources and latitude/salinity; and biological 
resources and uses/environmental impacts. 
Price” concluded that the method can be of value 
to managers and scientists alike, to determine 
associations between different environmental 
variables, and is especially useful for 



Photo: L. Murray 


Dugong feeding on seagrasses. 

Vousden” linked the extensive seagrass beds 
surrounding Bahrain to juvenile stages of commercially 
important penaeid shrimp and to a number of adult fish 
species, e.g. Siganus spp., a popular local food 
resource. Seagrasses also provided a habitat for the 
settlement of high densities of pearl oyster spat 
(Pinctada sp.), an important commercial species in 
Bahrain. Vousden"” reported a herd of 700 dugongs at 
one location over seagrass beds in Bahrain. 

Jones"! stated that seagrasses were sometimes present 
in the upper subtidal zone (2-3 m deep) along the Saudi 
Arabian coast as a band some 1-20 m wide. In these 
situations, seagrasses were recorded at 57 percent of 
the shore sites inspected, but seldom in luxuriant 
stands. The report estimated an areal extent of sea- 
grasses along Saudi Arabia of 370 km’. De Clerck and 
Coppejans™ studied seagrass distribution in the Gulf 
sanctuary between Ras az-Zaur and the northeast point 
of Abu Ali. They found that Halodule uninervis formed 
extensive meadows from the low-water mark to 3 m 
deep. Locally, it was replaced by Halophila ovalis and 
Halophila stipulacea. In some places near Dawhat Ad 
Dafi, seagrass cover declined rapidly below 3 m deep. 
At the Jubail Marine Wildlife Sanctuary (Saudi 
Arabia), Richmond! found that Halodule uninervis was 
again the dominant species, with the best developed 
beds at 3-4 m deep. Both species of Halophila were 
also found. Seagrasses were not found below 5 m. 
Vousden” mapped the seagrasses of Bahrain 
using satellite imagery. He reported that, as far as 
percentage cover was concerned, seagrass beds were 
the major soft-bottom habitat type within the 2-12 m 
subtidal zone. He found areas where the seagrasses 
went to 14 m deep. Seagrass distribution was 

widespread around the islands, covering most of the 
east coast, from south of Fasht Adhm to the Hawar 
Islands. Seagrasses also covered significant areas 
around Fasht Jarim and along the west coast, south 
and north of the Saudi-Bahrain causeway and along the 
southwestern coast. He also reported that the seagrass 
beds died back to low cover in winter, but found the 
beds to be healthy in March 1986. He concluded that the 
majority of well-developed beds occurred to the 
southeast of Bahrain. Halodule uninervis was the most 
common species. In summer, Halodule uninervis cover 
was as high as 90 percent. More than 50 percent of the 
sites at which seagrasses occurred supported 40 
percent or greater cover. 

In the UAE, Phillips et al."* performed an 
extensive study of seagrass distribution and extent of 
growth in 1999 and 2000. Halodule uninervis was the 
most abundant species in the Gulf waters of the UAE. 
Seagrasses occurred from 1.5 m to 15 m deep. Even 
though Halodule uninervis was occasionally found at 15 
m deep, Halophila ovalis tended to become the 
dominant species in depths greater than 11 m. 
Extensive continuous meadows were found wherever 
water depths were suitable {for Halodule uninervis 
from 1.5m to 11 m deep). Digitized estimates show that 
there were 5500 km’ of seagrasses in the Gulf waters 
of Abu Dhabi Emirate. 


Sheppard et al” listed a variety of coastal and marine 
uses and their major environmental impacts which 
affect or could affect seagrasses in the Gulf. They 
ranked them as short-term to medium-term impacts, 
medium-term to long-term impacts, and possible 
longer-term impacts. 

Except for my own observation on the effects of oil 
globules and oily black films over the bottom near an oil 
processing plant west of Jabel Dannah [seagrasses 
absent under the films], none of the literature records 
any negative impacts from oil-related pollution in the 

Vousden" stated that the agricultural industry 
was one of the major sources of organic non- 
petrochemical pollution to the marine environment. He 
found that the agricultural sector contributed 50 
percent of the total biological oxygen demand (BOD) 
loading to the waters around Bahrain. An oil refinery 
discharged 19 percent of the loading, with domestic 
discharges amounting to some 25 percent. The 
remaining discharges came from other industries. 

Sheppard et al." stated that coastal reclamation 
and dredging represented one of the most significant 
impacts on the coastal and marine environments of 
the Arabian region. They reported that coastal 
development and infilling have been far greater along 

Case Study 6.3 

The Arabian Gulf and Arabian region 


The seagrass beds in the Gulf are home to the world’s 
second largest assemblage of endangered dugongs 
(Dugong dugon) - upwards of 7000 individuals” (the 
largest population is off the coast of Australia], 
distributed mostly in the southern and southwestern 
regions of the Gulf. The dugongs belong to the 
monotypic order Sirenia and are the only herbivorous 
marine mammals, feeding directly on seagrasses. 
They can live to be 70 years of age and grow to over 3 
m in length and 400 kg in weight. Their nearest living 
non-sirenian relative is believed to be the elephant. 
Dugongs have extremely low reproductive capacities 
as they do not become sexually mature until about ten 
years of age, with subsequent calving only occurring 
at intervals of seven or more years. 

The most important foraging habitats for 
dugongs in the Gulf are on either side of Bahrain, off 
Saudi Arabia between Qatar and the UAE, and off Abu 
Dhabi"!. Outside the Gulf, the nearest population is in 
the Gulf of Kutch, northern India, suggesting the Gulf 
population is genetically and physically isolated. Until 
some 30 years ago, dugongs formed the staple diet of 
many Gulf-bordering villages, and had been used for 
their leathery skin and fats rendered into oils’. This 
suggests that populations were significantly larger 
than at present, and further reduction in population 
size might adversely impact their chances of survival 


Significant populations of herbivorous green turtles 
(Chelonia mydas} also depend on the seagrasses of 
the Gulf. They nest on Karan and Jana Islands off the 
Saudi Arabian coast {ca 1000 females/year)™, 
outside the Gulf at Ras Al-Hadd, Oman (ca 4000 
females/year]", and to a smaller extent off the 
southern coast of Iran, and are believed to feed 
among the seagrass pastures bordering the 
southern Gulf. Evidence of this is supported by re- 
cent tag returns from Saudi Arabia and Oman" *”. 
The green turtles in the Gulf also have low repro- 
ductive capacities, with estimates of sexual 
maturation periods of 15-40 years, and a survival 
rate of hatchlings of roughly only one in a thousand. 
These turtles have several key physiological features 
that set them apart from other Testudines, such as 
non-retractile limbs, extensively roofed skulls, limbs 
converted to paddle-like flippers, and salt glands to 
excrete excess salt. As with other reptiles, the sex of 
hatchlings is dependent on temperature during 

incubation, Adults can reach over 1 m in length 
and weigh over 190 kilograms, and feed nearly 
exclusively on seagrasses. The Gulf green turtles 
exhibit strong nesting site fidelity, returning to the 
same beaches to nest within and over several 
seasons". This fidelity coupled with a relatively low 
emigration rate from the Gulf, other than to the 
Omani nesting site, suggests that populations which 
nest and feed within the Gulf are, much as the 
dugongs, genetically and physically isolated. 

Threats to the turtle populations in the Gulf 
include moderate egg and adult harvesting, 
mortality in commercial and artisanal fishing gears, 
loss of nesting habitats, and significant loss or 
alteration of foraging grounds. While most Gulf- 
bordering nationals do not generally eat turtles or 
their eggs, many fishing boat crews are being 
replaced with a number of other nationalities who 
do, and unless the nesting beaches are patrolled the 
fishermen frequently dig up clutches of eggs. 
Fishermen are also known to take adults on an 
opportunistic basis”. An important modern impact 
is the extensive dredging and landfilling projects of 
several Gulf-bordering nations, which are altering or 
completely destroying foraging [seagrass) pastures. 
As in the case of the dugongs, the seagrasses upon 
which the green turtles in the Gulf depend are of 
Supreme importance to the survival of these 
isolated, regionally important populations. 


Based on the genetic isolation and population sizes 
of these two species, a recent meeting of experts in 
Hanoi, Viet Nam, concluded that the Gulf seagrass 
habitats are of outstanding universal value at a 
global level, and recommended they should be 
protected through international instruments such as 
the World Heritage Convention. Although there are a 
number of national conservation programmes and 
regional initiatives, they tend to be species-specific 
and not, as yet, directed at preserving marine habi- 
tats other than coral reefs. There is a need for 
focused attention on the remaining habitats, par- 
ticularly seagrass pastures, if the populations of 
dugongs and green turtles are to survive. 

Nicolas J. Pilcher 
Community Conservation Network, P.O. Box 1017, Koror, Republic of 



Photo: R.C. Phillips 


Halodule uninervis, Abu Dhabi area 

the Gulf coast than in the Red Sea or other parts of the 
Arabian region". 

IUCN"! and Sheppard and Price’ reported that 
approximately 40 percent of the Saudi Arabian coast 
had been developed, involving extensive infilling and 
reclamation. They found that conditions were similar in 
other Gulf States, such as Bahrain and Kuwait. More 
than 30 km’ (3306 ha) of Bahrain was either reclaimed 
or artificial land'*"'. In the late 1980s, there were plans 
for further infilling on an area of almost 200 km’ in 
Bahrain”. | have observed extensive dredging 
activities around the UAE. These activities involved 
maintenance channel dredging, dredging for new 
channels and land reclamation. They were being 
carried out inshore in the most extensive continuous 
seagrass beds in Abu Dhabi Emirate. 

Price” noted that dredging and coastal infilling 
projects were occurring throughout Saudi Arabia, e.g. 
Tarut Bay and the Jubail area, and also in Bahrain and 
Kuwait. He conjectured that such activity was likely to 
affect not only the shrimp and fish stocks, but also the 
ecology of coastal habitats generally. 

Vousden" stated that the effects of coastal 
development represented a significant problem to the 
marine environment of Bahrain. He noted that the 
shallow intertidal flats next to a reclamation site 
became smothered in a thick glutinous silt often many 
centimeters deep and of little biological value due to its 
anoxic nature. Offshore, the benthic communities 
became choked by the anoxic sediments. Primary 
productivity was reduced drastically by the high 
sediment loads and consequent increase jn water 
turbidities. Price et al’ noted that seagrass had 
become smothered as a result of the sedimentation 
caused by dredging. 

Thus, many studies have recorded the large-scale 
and continuing dredging and land reclamation projects 

throughout the Gulf States. However, no one has 
documented the amount of historical loss of 
seagrasses as a result of this activity. Such studies are 
needed. The study of Phillips ef al." in the UAE 
appears to be the only study that has precisely 
documented the extent of seagrass distribution in any 
of the Gulf States. Such studies are also needed. 


Each Gulf State has a varying number of authorities 
designed to study and/or protect seagrasses. However, 
one can still see massive and continuing dredging and 
land reclamation in all countries. Since there is so little 
effective cooperation between the states as concerns 
marine conservation of seagrasses, the feeling within 
the Gulf is that this conservation and protection effort 
would be best accomplished at the regional level. There 
is a plan, the Kuwait Action Plan [KAP], based on the 
Kuwait Regional Convention for Cooperation on the 
Protection of the Marine Environment from Pollution. 
All countries within the KAP region are signatories of 
the convention. |IUCN/UNEP"' reported that the priority 
concern was the current extensive loss or severe degra- 
dation of seagrass habitats, and the probable reduction 
in natural resources associated with this habitat. 

The reports of Price’, the Coral Reef and Tropical 
Marine Research Unit’! and Price et al.’ contained 
detailed recommendations for conserving seagrass 
beds in the Gulf area. These focused largely on 
preventing further uncontrolled habitat destruction and 
widespread pollution. IUCN/UNEP"! concluded that any 
legislation aimed at preventing impacts must be 
followed by enforcement. Little has been done to 
implement these recommendations. Except for the 
UAE, none of the countries has taken any steps to 
implement the beginning of an effective management 
program that would start with baseline mapping, 
followed by periodic monitoring and mapping efforts. 
The distribution and rate of seagrass loss needs to be 
determined in the various KAP countries. As of 1985, 
the conservation status of seagrass habitats had been 
considered in Bahrain’! and Saudi Arabia’ *", but not in 
detail in any of the other KAP countries. 

Sheppard et al." stated that in addition to the 
UNEP Regional Seas Programme, there were other 
regional agreements, including those of the GCC (Gulf 
Cooperative Council], the GAOCMAO (Gulf Area Oil 
Companies Mutual Aid Organisation] and others. These 
agreements relate to environmental management and 
pollution control. 


Ronald C. Phillips, Florida Marine Research Institute, 100 Eighth 
Avenue, S.E., St Petersburg, Florida 33701, USA. Tel (home): +38 (0) 692 
413086. E-mail: ronphillips67( 

The Arabian Gulf and Arabian region 81 



JUCN/UNEP [1985]. The Management and Conservation of 
Renewable Marine Resources in the Indian Ocean Region in the 
Kuwait Action Plan Region. UNEP Regional Seas Reports and 
Studies No. 63. 63 pp. 

Sheppard CRC, Price ARG, Roberts C [1992]. Marine Ecology of the 
Arabian Region. Academic Press, London. 359 pp. 

Basson PW, Burchard JE, Hardy JT, Price ARG [1977]. Biotopes of 
the Western Arabian Gulf. Aramco, Dhahran. 284 pp. 

Jones DA [1985]. The biological characteristics of the marine 
habitats found within the ROPME Sea Area. Proceedings of ROPME 
Symposium on Regional Marine Pollution Monitoring and Research 
Programmes |ROPME/GC-4/2). pp 71-89. 

Vousden DHP [1988]. The Bahrain Marine Habitat Survey. Vol. 1. 
The Technical Report. ROPME. 103 pp. 

Price ARG [1982]. Conservation and Sustainable Use of Natural 
Resources. Part II. Marine. Report for IUCN/MEPA for the Expert 
Meeting of the Gulf Coordinating Council to review environmental 

Price ARG, Chiffings TW, Atkinson MJ, Wrathall TJ [1987]. 
Appraisal of resources in the Saudi Arabian Gulf. In: 

Magoon OT, Converse H, Miner D, Tobin LT, Clark D, Domurat G 
(eds) 5th Symposium on Coastal and Ocean Management. 

Vol. 1. American Society of Coastal Engineers, New York. pp 1031- 

Vine PJ [1986]. Pearls in Arabian Waters. Immel Publishing, 
London. 59 pp. 

Preen A [1989]. The Status and Conservation of Dugongs in the 
Arabian Region. Vol. 1. MEPA Coastal and Marine Management 
Series Report No. 10. Meteorological and Environmental Protection 
Administration. Jeddah. 200 pp. 

Jupp BP, Durako MJ, Kenworthy WJ, Thayer GW, Schillak L [1996]. 
Distribution, abundance and species composition of seagrasses at 
several sites in Oman. Aquatic Botany 53: 199-213. 

Lipkin Y [1977]. Seagrass vegetation of Sinai and Israel. In: McRoy 
CP, Helfferich C (eds) Seagrass Ecosystems: A Scientific 
Perspective. Marcel Dekker, New York. pp 263-293. 

Aleem AA [1979]. A contribution to the study of seagrasses along 
the Red Sea coast of Saudi Arabia. Aquatic Botany 7: 71-78. 
Hulings NC [1979]. The ecology, biometry, and biomass of the 
seagrass Halophila stipulacea along the Jordanian coast of the Gulf 
of Aqaba. Botanica Marina 22: 425-430. 

Jacobs RPWM, Dicks B [1985]. Seagrasses in the Zeit Bay and at 
Ras Gharib {Egyptian Red Sea coast). Aquatic Botany 23: 137-147. 
Hulings NC, Kirkman H [1982]. Further observations and data on 
seagrasses along the Jordanian and Saudi Arabian coasts of the 
Gulf of Aqaba. Tethys 10: 218-220. 

Jones DA [2002]. Personal communication. 

Price ARG [1990]. Rapid assessment of coastal zone management 
requirements: Case study in the Arabian Gulf. Ocean and Shoreline 
Management 13: 1-19. 

Phillips RC, Loughland RA, Youssef A [Submitted manuscript]. 
Seagrasses of Abu Dhabi Emirate, United Arab Emirates, Arabian 
Gulf. Tribulus. 

Price ARG, Coles SL [1992]. Aspects of seagrass ecology along the 
western Arabian Gulf coast. Hydrobiologia 234: 129-141. 
Kenworthy WJ, Durako MJ, Fatemy SMR, Valavi H, Thayer GW 
[1993]. Ecology of seagrasses in northeastern Saudi Arabia one 
year after the Gulf War oil spill. Marine Pollution Bulletin 27: 




















Durako MJ, Kenworthy WJ, Fatemy SMR, Valavi H, Thayer GW 
[1993]. Assessment of the toxicity of Kuwait crude oil on the 
photosynthesis and respiration of seagrasses of the northern Gulf. 
Marine Pollution Bulletin 27: 223-227. 

Wahbeh MI [1980]. Studies on the Ecology and Productivity of the 
Seagrass Halophila stipulacea, and Some Associated Organisms in 
the Gulf of Aqaba (Jordan). D.Phil. thesis, University of York. 

Jones DA, Ghamrawy M, Wahbeh MU [1987]. Littoral and shallow 
subtidal environments. In: Edwards A, Head SM [eds) Red Sea. 
Pergamon Press, Oxford. pp 169-193. 

Price ARG, Vousden DHP, Ormond RFG [1983]. Ecological Study of 
Sites on the Coast of Bahrain, with Special Reference to the Shrimp 
Fishery and Possible Impact from the Saudi-Bahrain Causeway 
under Construction. IUCN Report to the UNEP Regional Seas 
Programme. Geneva. 

Coles SL, McCain JC [1990]. Environmental factors affecting 
benthic communities of the western Arabian Gulf. Marine 
Environmental Research 29: 289-315. 

McCain JC [1984]. Marine ecology of Saudi Arabia. The nearshore, 
soft bottom benthic communities of the northern area, Arabian 
Gulf, Saudi Arabia. Fauna of Saudi Arabia 6: 102-126. 

Vousden DHP, Price ARG [1985]. Bridge over fragile waters. New 
Scientist No. 1451: 33-35. 

De Clerck 0, Coppejans E [1994]. The marine algae of the Gulf 
Sanctuary. In: Establishment of a Marine Habitat and Wildlife 
Sanctuary for the Gulf Region. Final Report for Phase Ill. Jubail and 
Frankfurt. CEC/NCWCD. pp 254-280. 

Richmond MD [1996]. Status of subtidal biotopes of the Jubail 
Marine Wildlife Sanctuary with special reference to soft-substrata 
communities. In: Krupp F, Abuzinada AH, Mader IA leds) A Marine 
Wildlife Sanctuary for the Arabian Gulf. Environmental Research 
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Riyadh and Seneckenberg Research Institute, Frankfurt. 

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Gulf? New Scientist 1759: 36-40. 

Madany IM, Ali SM, Akter MS [1987]. The impact of dredging and 
reclamation in Bahrain. Journal of Shoreline Management 3: 

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Sea Area. UNEP Regional Seas Reports and Studies. No. 112. Rev. 
1. UNEP, Nairobi. 

TMRU [1982]. Management Requirements for Natural Habitats and 
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mydas in the Arabian Gulf. Chelonian Conservation & Biology 3: 

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Al-Ghais. Personal communication. 

As-Saady. Personal communication. 

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and Maderson PEA leds} Biology of the Reptilia, Vol. 14. John Wiley 
& Sons. pp 269-328. 

Miller JD [1989]. Marine Turtles, Volume 1: An Assessment of the 
Conservation Status of Marine Turtles in the Kingdom of Saudi 
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MEPA, Jeddah. 289 pp. 



7 The seagrasses of 


productive coastal and marine ecosystems in the 

East African region. The Kenyan (600 km) and 
Tanzanian (800 km) coastlines have a shallow and 
relatively narrow continental shelf bordering the Indian 
Ocean and are characterized by extensive fringing coral 
reefs, several sheltered bays and creeks, limestone 
cliffs, mangrove forests, sand dunes and beaches'”. 
The tidal amplitude is rather large - up to 4 m near 
Mombasa” - and therefore there is a fairly extensive 
intertidal zone between the fringing reefs and the coast 
in many places. The substrate in this zone consists 
mainly of carbonate sands derived from eroding reefs. 
The productivity of these intertidal areas is determined 
predominantly by the presence of seagrasses and 
macroalgae, which grow wherever shallow depressions 
retain a covering of water during low tide. 

The most extensive seagrass meadows occur in 
back-reef lagoons, which are found between the 
beaches or cliffs and the adjacent fringing reefs. 
Narrow channels connect the lagoons with the sea 
during low tide, but high-tide waters pass over the reef 
crest into the lagoon. Apart from many fish species that 
reside permanently inside such lagoons, many other 
species feed there during high tide, leaving for deeper 
offshore waters during the ebbing tides. 

At several places along the East African coast, 
these lagoons grade into sheltered semi-enclosed bays 
(e.g. at Mida, Kilifi, Mtwapa, Tudor, Gazi and Funzi in 
Kenya, and at Tanga, Bagamoyo, Mohoro, Kilwa and 
Mtwara in Tanzania) where mangroves, seagrass 
meadows and coral reefs occur as adjacent and 
interrelated ecosystems. Where the supply of 
terrigenous sediments is limited, seagrass vegetation 
is also common in the creeks and channels that run 
through the mangroves, possibly functioning as traps 
and reducing the extent of the fluxes of particulate 
matter and nutrients between the mangroves and the 
ocean. In Gazi Bay (Kenya), for example, it is possible to 

S eagrasses are a major component of the rich and 

C.A. Ochieng 
P.L.A. Erftemeijer 

snorkel in creeks and small rivers inside the 
mangroves, where the water is very clear and the 
bottom is covered in a luxuriant growth of seagrasses. 
In the delta areas of major rivers, such as the Tana 
River in Kenya and the Rufiji River in Tanzania, 
seagrass growth is minimal. 


The following 12 seagrass species have been 
encountered during several studies in Kenya and 
Tanzania“: Halodule uninervis, Halodule wrightii, 
Syringodium isoetifolium, Cymodocea_ rotundata, 
Cymodocea serrulata, Thalassodendron ciliatum, 
Zostera capensis, Enhalus acoroides, Halophila minor, 
Halophila ovalis, Halophila stipulacea and Thalassia 
hemprichii. All species appear to be widely distributed 
along the entire coastline of both countries, even those 
with only a limited number of observations, such as 
Zostera capensis, Halophila minor and Halophila 
stipulacea. Seagrasses often occur in mixed 
communities consisting of two to several of the 12 
species. Thalassodendron ciliatum is often the most 
dominant species, forming pure stands with high 
biomass. Three additional seagrass species (Halodule 
pinifolia, Halophila ovata and Halophila beccarii) have 
been reported for the region” '”, but these observations 
may constitute misidentifications and need further 

There is some controversy over the occurrence of 
the species Halodule wrightii in East Africa. Most 
authors have included Halodule wrightii in their species 
descriptions for the region based on leaf width and tip 
morphology““®!. However, field observations in Florida” 
indicated that leaf tips in Halodule spp. vary widely from 
bicuspidate to tridentate on shoots of the same 
rhizome. Experimental culture!” revealed that leaf tips 
of Halodule are environmentally variable, related to 
nutrient variability or tidal zone. Furthermore, isozyme 
analyses of diverse collections throughout the tropical 

> Lamu Island 

Mambrui + 

: Ungwana Bay 
Malindi \ \e Formosa Bay 
Mida Creek~_~e 
*___ Watamu Manne 

National Park 

Bamburi 4° 
~_ Mombasa Marine National 

~ Park and Reserve 


Mombasa ¢ 
Gazi Bay. 

v« Diani-Chale Lagoon 

#é Kilindini 
=" Pemba Island 


° B- Chwaka Bay 

% Dar es Salaam 




Mohoro e 

+ 2" Mafia Island 

0 40 80 120 160 200 Kilometers Mtwara® 

Map 7.1 
Kenya and Tanzania 

western Atlantic as well as the Indo-Pacific revealed a 
clear genetic difference between the two ocean 
systems, but genetic uniformity within each of the two 
ocean systems'”’. Based on these results it was 
concluded that all plants {with this morphology] from 
the Indo-Pacific are Halodule uninervis while those in 
the tropical western Atlantic are Halodule wrightii"”. 
Nevertheless, Halodule wrightii continues to be 
reported in literature despite these field, culture and 
isozyme findings'’ '” '”'. It appears therefore that there 
is a need for further analyses of chromosomal 
differences and physiological studies to determine the 
relationship between nutrients and leaf morphology of 
Halodule species. 

The seagrass beds in East Africa, as indeed 
elsewhere, harbor a diverse array of associated plant 
and animal species. Detailed studies on seagrass 
associates in this region have identified over 50 
species of macroalgae and 18 species of algal 
epiphytes” at least 75 species of benthic 
invertebrates?" especially gastropods and 
bivalves - several species of sea cucumbers” and at 
least seven sea urchin species”, various shrimp, 
lobster and crab species”** and over 100 fish 
species’’*” in association with seagrass beds. This 
clearly underscores the importance of seagrass 
meadows for biodiversity conservation. 

Kenya and Tanzania 

Seagrass beds in the region also support sizeable 
populations of two endangered species, i.e. the green 
turtle Chelonia mydas®”*' and the dugong Dugong 
dugon”'***”, both of which feed on seagrasses. In 1994, 
a total of 443 sea turtles was recorded along the 
Kenyan coast, among which the green turtle was by far 
the most common species’. In Tanzania, there are no 
recent population studies®". Similar surveys along the 
Kenyan coast revealed ten dugongs during November 
1994 and six dugongs during February-March 1996, 
representing a significant decline in comparison to 
earlier counts of over 50 animals in the 1960s and 
1970s'":*”. The most important dugong habitat in Kenya 
can be found in the Lamu Archipelago. In Tanzania, the 
main centers of dugong population have been reported 
along the Pemba-Zanzibar channels and in the Rufiji- 
Mafia area’. The need for protection and management 
of sea turtle and dugong habitats (seagrass beds] has 
been stressed”. 

The importance of East African seagrass 
ecosystems for fisheries is gradually emerging from an 
increasing research effort on the role of the seagrass 
meadows in this region as nursery, breeding and 
feeding grounds for marine fish and crustacean species 
of economic importance such as shrimps [Penaeus] 
and spiny lobster (Panulirus)'”***". Several fish species 
graze on seagrasses, notably rabbitfishes (Siganidae] 
and surgeonfishes (Acanthuridae}, while parrotfishes 
(Leptoscarus spp.) preferentially graze the epiphytes 
on the seagrass. Adult fishes, such as snappers, 
groupers, grunts and barracuda, feed on the infauna of 
seagrass beds while the diet of their juvenile stages is 
mainly seagrass-derived detritus. Portunus pelagicus, 
an important contributor to the crab fishery in 
Bagamoyo and Dar es Salaam, is said to inhabit shallow 
coastal habitats such as estuaries, sheltered bays and 
open sublittoral waters (all of which may include 
seagrass], where all stages of its life cycle are found”. 

Significantly higher fish abundance and catch 
rates were found in seagrass beds in comparison to 
bare sand areas in a study of dema trap fishery in the 
coastal waters of Zanzibar, Tanzania’. Similarly, 11 of 
the 99 fish species of Tudor Mangrove Creek {Kenya} 
are typically associated with seagrass (6 percent of the 
total catch)”, while 74 species of fish (in a total of 39 
families) and 15 species of macro-crustaceans were 
reported for the seagrass beds of Chwaka Bay and Paje 
on Zanzibar”. At both of these latter sites, Gerres 
oyena was the dominant fish species in the seagrass 
beds (>60 percent of the total catch). 

Harvesting of bivalves (notably Anadara antiquata, 
Anadara natalensis and Anadara uropigilemana, 
Gardium assimile, Gardium pseudolina, Gardium 
flavum and Scapharca_ erythraeonensis) and 
gastropods (including Murex ramosus, Pleuroploca 

fy gl 


WI Fe 





Case Study 7.1 

Gazi Bay, a semi-enclosed bay (15 km’) ca 50 km 
south of Mombasa, Is characteristic of the creeks and 
bays along the East African coastline. Mangroves, 
seagrass meadows and coral reefs occur here as 
adjacent ecosystems. Mangroves are found along 
small seasonal rivers on the landward side of the bay 
and are drained by two tidal creeks. Extensive sea- 
grass vegetation is common among and between the 
mangroves, where it functions as a trap reducing the 
flux of sediment, organic material and nutrients from 
the mangroves to the ocean. Snorkeling in creeks and 
small rivers among the mangroves can be a sens- 
ational experience: the water can be very clear and 
the bottom is covered in a luxuriant growth of 
seagrasses, traversed by mangrove roots where 
schools of juvenile fish hide from predators. Adjacent 
to the mangroves on the seaward side are intertidal 
flats, intersected by some channels, and shallow 
subtidal areas which stretch to the fringing reef. Most 
of this area is covered by various species of sea- 
grasses and macroalgae, with the exception of a few 
sandy patches” '. Seagrasses in Gazi Bay cover an 
estimated total area of approximately 8 km*. The 
maximum tidal range in Gazi Bay is 250 cm. 

All the 12 seagrass species of eastern Africa 
are found in Gazi Bay. Macroalgae are among their 
most conspicuous floral associates. Sixteen species 
of Chlorophyta, 4 species of Phaeophyta and 31 
species of Rhodophyta associated with seagrass beds 
in Gazi Bay have been identified®!. Among these were 
Euchema, Gracilaria, Ulva and Sargassum, all of 
which include species of potential economic value. 
Average leaf production of Thalassodendron ciliatum, 
the most dominant seagrass species, ranges from 
4.9 to 9.5 g/m?/day”"""”. A separate study of the growth 
and population dynamics of Thalassodendron 
ciliatum has shown that its vertical growth is the 
fastest reported for any seagrass to date [42 inter- 
nodes, i.e. 42 leaves/year), whereas the horizontal 
growth rate (16 cm/year] is among the slowest'*”. As 
a result of the slow horizontal rhizome growth, shoot 
recruitment through branching of vertical shoots is 
an important part of the clonal growth of this 
population and so an essential component of the 
production of Thalassodendron ciliatum. 

Seagrass meadows are open systems subject 
to nutrient impoverishment due to export processes 
mediated by tidal inundation. The intriguing feature of 
the occurrence, in very close proximity to one 
another, of mangroves, seagrasses and corals in Gazi 

Bay attracted scientists to study the interlinkages 
between these systems in terms of dissolved 
nutrients and seston fluxes as well as shuttle move- 
ments of fish”. Analysis of the stable isotope signa- 
ture of the sediment carbon in the seagrass zone 
revealed significant carbon outwelling from the man- 
groves, but deposition of particulate organic matter 
rapidly decreased with distance from the forest, with 
most litter trapped within 2 km of the mangroves”. 
However, marked decreases in the carbon signature 
of seston flowing over the seagrass zone during flood 
tides pointed to a reverse flux of organic particles 
from the seagrass zone to the mangroves, with the 
nearby coral reefs existing in apparent isolation. 
Direct flux measurements of both mangrove and 
seagrass litter showed that trapping of mangrove 
litter by adjacent seagrasses is reciprocated by a 
retention of seagrass litter in the mangrove, and this 
give-and-take relationship is mediated by tides. 
Further research has indicated that the detrital 
cycling in the inner parts of the mangrove forest 
forms part of a rather closed system based on local 
inputs, whereas cycling in the outer parts of the forest 
is tightly connected with the adjacent seagrass 
ecosystem. Despite the presence of tide-mediated 
chemical fluxes which allow one system to influence 
another, the input of mangrove carbon did not co- 
incide with enhanced leaf production of the dominant 
subtidal seagrass Thalassodendron  ciliatum'*'. 
Presumably, carbon outwelling from the mangrove 
coincides with only limited export of nitrogen and 
phosphorous, and the restricted effects of these 
nutrients on the seagrass [if any] are masked by other 
local factors. 

Gazi Bay is typical of the major fishing grounds 
in Kenya, most of which are located in shallow near- 
coastal waters due to a lack of sophisticated gear and 
motorized boats which would allow exploitation of 
deeper waters. Carbon isotope and delta '°N studies 
into trophic relationships in Gazi Bay allowed the 
identification of three trophic levels, i.e. herbivores, 
zoobenthiplanktivores and piscivores/benthivores. 
Seagrass beds were found to be the main feeding 
grounds providing food for all fish species studied in 
Gazi Bay, Kenya”. Seagrass plants were the major 
source of carbon for four fish species studied in the 
bay. They also contribute [together with mangroves) 
to the particulate organic carbon for prawn larvae, 
zooplankton, shrimps and oysters, hence their 
support for food webs”. 

trapezium and Oliva bulbosa) for food is common on 
many of the intertidal areas (with or without seagrass) 
in Tanzania. No data currently exist on the quantities 
collected from seagrass areas. Strombus gibberulus, 
Strombus trapezium and Cypraea tigris, all of which 
are popular curio goods, are common in seagrass 
areas around Dar es Salaam”. Twenty species of sea 
cucumbers, the most common of which are Holothuria 
scabra, Holothuria nobilis, Bohadschia_ vitiensis, 
Bohadschia argus, Thelenota anax, Stichopus 
chloronotus, Stichopus variegatus and Stichopus 
hemanni, are harvested from intertidal areas [including 
seagrass beds] along the Tanzania coast for export’? *”. 


Studies on the ecological processes and functioning of 
seagrass ecosystems in Kenya and Tanzania have 
provided a better understanding of the natural factors 
limiting the growth and geographical distribution of 
seagrasses, environmental stresses and indirect 
values of seagrass ecosystems in this region. 

Leaf productivity of Thalassodendron ciliatum 
ranges from 4.9 to 9.5 g/m’/day”'''“"!, Vertical growth 
rates of Thalassodendron ciliatum (42 internodes, i.e. 
42 leaves/year] measured in Kenya are among the 
fastest reported for any seagrass species to date, 
whereas its horizontal growth rates (16 cm/year) rank 
among the slowest'. Shoot recruitment rates 
measured in seagrass meadows along the coasts of 
Kenya and Zanzibar were either the same as or larger 
than shoot mortality rates, suggesting that the 
environmental quality in this region is still suitable for 
sustaining vigorous seagrass vegetation”. 

Most factors that govern primary production, 
including light and temperature, are relatively constant 
throughout the year in this region. However, the 
composition of the oceanic water and the amount of 
freshwater which enters the coastal areas are variable. 
At several sites along the coast substantial seepage of 
freshwater occurs, as a result of which brackish water 
is often found in areas of seagrass beds”. Using 
nitrogen stable isotope signatures, groundwater was 
found to influence seagrass species diversity and 
abundance where’ Thalassodendron  ciliatum 
dominated high groundwater outflow areas as opposed 
to Thalassia hemprichii. 

Photosynthetic studies carried out in Zanzibar, 
Tanzania, indicate that seagrasses may respond 
favorably to any future increases in marine carbon 
dioxide levels due to global climate change“* “. The 
enhanced photosynthetic rates by Halophila ovalis and 
Cymodocea rotundata in the high, frequently air- 
exposed, intertidal zone may have been related to a 
capacity to take up the elevated HCO, levels directly”. 
Furthermore, these tropical intertidal seagrasses were 

Kenya and Tanzania 

found to be more sensitive to desiccation than subtidal 
seagrasses with the exception of the species 
Syringodium isoetifolium“”. Desiccation tolerance, 
however, may not be a trait that determines the vertical 
zonation of tropical seagrasses. The ability to tolerate 
high irradiances, as well as the high nutrient inputs 
from the shore, apparently allows the shallow species 
to occupy the uppermost intertidal zone. 

Seagrass beach cast material may contribute 
significantly to beach stability, as implied by a study 
along the Kenyan coast’ “‘! [see Case Study 7.2). 

Detailed studies in Gazi Bay, Kenya, revealed 
significant carbon outwelling from the mangroves into 
the adjacent seagrass meadows and a reverse flux of 
organic particles from the seagrass zone to the 
mangroves, with nearby coral reefs existing in apparent 
isolation’ as far as particulate organic matter is 
concerned. Export of organic matter from mangroves in 
Chwaka Bay (Tanzania) was also limited to a narrow 
fringe of seagrasses immediately adjacent to the 
mangroves”. Despite the presence of tide-mediated 
chemical fluxes, which allow one system to influence 
another, the input of mangrove carbon did not coincide 
with enhanced leaf production of the dominant subtidal 
seagrass Thalassodendron ciliatum™. 

Carbon isotope and delta '°N studies on trophic 
relationships showed that seagrass beds were the 
main feeding grounds for all fish species studied in Gazi 
Bay, Kenya“’. An experiment on feeding preference 

showed that Calotomus carolinus (Scaridae), the 
second most abundant fish in Watamu Marine National 


The catch from a trap fishing trip in the seagrass beds - mainly the 
seagrass parrotfish Leptoscarus vaigiensis, some pink ear emperor 
Lethrinus lentjan, and a grouper Epinephelus flavocaeruleus. 


Photo: F. Gell 



Park, preferred pioneering short-lived seagrass 
species to climax species. The study also highlighted 
the role of grazing fish in influencing seagrass 

Sea urchins mediate the competitive success of 
different seagrass and fish species, in terms of 
distribution and abundance. Sea urchins can reduce 
grazing rates of some species of parrotfish'”, while the 
relative dominance of some of the sea urchin species 
indicates a high fishing pressure on herbivorous 
fish species”. Tripneustes gratilla, for instance, can 
graze at a rate of 1.8 seagrass shoots/m//day at fronts 
that support a sea urchin abundance of 10.4 
individuals/m*"“!. The species composition of seagrass 
communities in reef environments appears to be 
partially affected by prey choices of the dominant 
grazers. Parrotfishes and the sea urchin Echinothrix 
diadema appear to favor seagrass beds dominated by 
Thalassodendron ciliatum, while other sea urchin 
species such as Diadema setosum, Diadema savignyi 
and Echinometra mathaei favor areas high in Thalassia 

There have been few studies on western Indian 
Ocean seagrasses to date. A recent bibliographic survey 
of marine botanical research outputs from East Africa 
between 1950 and 2000 yielded only 44 papers and 
reports that dealt with seagrasses'". Even baseline data 
on distribution are largely lacking’. In recent years, 
however, the number of seagrass publications from 
studies in the region has increased and efforts are 
under way for integrated coastal zone management and 
participatory management of marine protected areas 
including seagrass beds, indicating a growing 
recognition of the important value of seagrass 

Massive beaching of seagrass litter was reported 
as early as 1969 by an expedition to Watamu on the 
Kenyan coast’, rendering it unlikely that these 
accumulations have increased over past or recent 

No direct utilization of seagrasses in East Africa 
has been reported’ except for anecdotal reference to 
the small-scale use of the leaves of Enhalus 
acoroides for weaving mats and thatching huts, and 
the harvesting of their rhizomes by people of the 
Lamu Archipelago in Kenya, who dry and then grind 
them into flour for cooking what is locally known as 
mtimbi*™'. Quantitative data on such direct uses as 
well as catch statistics of the seagrass-associated 
fisheries in this region are lacking, making it 
impossible to draw any conclusions regarding trends. 
There are no published data on estimates of area loss 
or degradation from the East African region’”*". At 
present, there are insufficient data for even a crude 


There are very few area estimates for seagrasses in 
this region. Distribution maps of seagrasses are only 
available for Mida Creek, Gazi Bay, Diani-Chale Lagoon 
and Chwaka Bay. The recent UNEP Atlas of Coastal 
Resources shows that seagrass beds occur throughout 
the 600-km-long Kenyan coastline in sheltered tidal 
flats, lagoons and creeks, with the exception of the 
coastal stretch adjoining the Tana Delta’. The testing of 
a remote-sensing methodology for seagrass mapping 
in southern Kenya estimated the net area of vegetation 
cover to be approximately 33.63 km’ within a stretch of 
around 50 km of coastline’. Ground-truthing revealed 
that most of these areas were dominated by pure 
stands of Thalassodendron ciliatum. 

Chwaka Bay on the eastern side of Unguja Island 
(Zanzibar), which covers more than 100 km’, has 
extensive mixed seaweed-seagrass areas, with 
seagrasses representing between 50 and 80 percent of 
the macroflora biomass”. In Gazi Bay, which covers 
approximately 15 km’, seagrass beds cover an area of 
approximately 8 km? from the lower margin of the 
mangrove forest through the intertidal and subtidal 
flats up to the fringing reef, with the exception of a few 
sandy patches”. The Diani-Chale Lagoon along the 
Kenyan coast measures roughly 6 km* with seagrass 
beds covering up to 75 percent’. The Nyali-Shanzu- 
Bamburi Lagoon, with a total area of approximately 20 
km’, is 60 percent covered by seagrass beds”. 

At present, there are insufficient data for even a 
“best guess” of total seagrass coverage in Kenya and 
Tanzania, but new mapping data are expected to 
become available from a recently started regional 
seagrass research project under the Marine Science for 
Management Programme (MASMA)]. 


The lack of a true continental shelf, stretching out no 
more than a few kilometers from the Kenyan and 
Tanzanian shores, makes the coastal resources all the 
more vulnerable to overexploitation and influences 
from activities on land'”’. In general, seagrasses 
appear to have experienced fewer direct negative 
impacts than mangroves or coral reefs in the region, 
but this may merely reflect the lack of any reliable 
(quantitative) data. Deepening of channels for ships at 
harbors results in uprooting and burial of seagrass 
plants by dredge-spoil™. 

Several beaches and adjacent coastal areas in 
Kenya and Zanzibar are under increasing pressure 
from expanding tourism development®”. High hotel 
density in close proximity to the beach is common”. 
Seagrass beds are locally damaged by motor boat 
propellers and anchoring in the waters near these 
highly intensive tourist areas'“’. While mooring buoys 

have been deployed within the marine park to protect 
the coral reef, the seagrass beds remain unguarded. In 
some areas very popular with tourists stretches of 
seagrass meadow (deemed a nuisance to swimmers] 
are cleared by cutting and/or uprooting’™’. In addition, 
the cumulative effects of raking, burying and removing 
seagrass beach cast material may have negative 
impacts on the functioning of the adjacent seagrass 

Direct destruction of seagrass vegetation occurs 
by trawling activities. Commercial trawlers operating in 
the Rufiji Delta, Mtwara and coastal areas between 
Bagamoyo and Tanga (Tanzania), as well as Ungwana 
Bay in Kenya {where they reportedly have a fishing 
effort well beyond the potential sustainable yield’, are 
non-selective and are destructive to the seabed. Illegal 
trawling - even during the closed season - occurs in 
Bagamoyo, Tanzania, where up to 80 percent of prawn 
bycatch is seagrass”. Trawling has also been reported 
as a major cause of mortality of the green turtle along 
the Kenyan coast"”.. Artisanal fishermen often connect 
separate navigable channels by digging through 
intertidal flats in order to make way for their canoes, 
causing damage to seagrass, albeit at a small scale’. 
Overfishing could pose a likely threat to seagrass 
communities, as has been reported for the coral reefs 
in this region®”, although there are no direct reports to 
confirm this. 

Recent agricultural activities in the Sabaki 
catchment have resulted in accelerated soil erosion 
and a tremendous increase in river sediments from 
some 58000 tons/year in 1960 up to as much as 7-14 
million metric tons/year at present”. Considerable 
amounts of sediment brought down by the river to the 
coral reefs and seagrass beds have been implicated in 
the low seagrass species composition at Mambrui'™’. 
The apparent absence of seagrass beds in Ungwana 
Bay and northern Rufiji Delta’: ’! might also be related 
to siltation by the Tana and Rufiji Rivers, but no studies 
have been conducted here. 

Oil pollution is one of the potential threats to 
seagrasses in East Africa owing to spillage of crude oil 
in harbors and the risk posed by a large fleet [over 200 
oil tankers per day) from the Middle East across the 
coastal waters. There have been no major oil spills to 
date, except in 1988 when 5000 metric tons from a 
pierced fuel tank in Mombasa destroyed a nearby area 
of mangroves and associated biotopes. The seagrass 
species Halophila stipulacea and Halodule wrightii 
have not reappeared at the site since the spill™!. In 
Tanzania, oil pollution along the coast - though not 
severe - is heaviest during the southwest monsoon""! 
The extent and specific effects of oil pollution on 
seagrass ecosystems in East Africa's largest harbors, 
Kilindini and Dar es Salaam, especially in creeks and 

Kenya and Tanzania 

Impacts of tourism industry on seagrasses. Seagrass cover has 
declined in front of a Mombasa north coast beach hotel 

sheltered lagoons, may be high but remain uninves- 
tigated to date. 

Increasing populations in coastal towns and 
cities, such as Mombasa, Malindi and Dar es Salaam, 
present a potential (but localized) threat to the coastal 
seagrass resources from domestic solid waste, sewage 
disposal and dredge spoil dumping, all of which are 
responsible for the declining water quality”. Seasonal 
blooming of Enteromorpha and Ulva species occurs 
locally, especially in areas close to sewage discharge 
points from hotel establishments and municipal 
sewage”), Although low organic loading is a feature 
of the well-flushed lagoon system, eutrophic conditions 
and high bacterial contamination in the sheltered and 
semi-enclosed creeks have been reported’. 
Significant heavy metal pollution from urban and 
industrial effluents has been reported in coastal waters 
around Dar es Salaam", affecting edible shellfish 
populations’. Reclamation of tidal flats, such as 
proposed by the Selander Bridge coastal waterfront 
reclamation project in Dar es Salaam, constitutes 
another potential threat to seagrass ecosystems. 

The expanding open-water mariculture farms of 
the seaweed Eucheuma spinosa currently cover around 
1000 ha of intertidal area on Zanzibar (Tanzania). The 
various adverse effects that seaweed farming has on 
intertidal areas could well mar the positive picture of its 
socioeconomic benefits to coastal people. A marked 
decline in seagrass cover from physical clearing of 
seagrass vegetation by seaweed farmers has been 
reported’. Seaweed farming areas on Zanzibar appear 

Photo: PL.A. Erftemeijer 




Case Study 7.2 


The Mombasa Marine National Park and Reserve 
(Kenya] encompasses a major part of the Nyali- 
Shanzu-Bamburi Lagoon (20 km’) which has a 
maximum depth of 6 m. It is bordered by white 
sandy beaches on the landward and a fringing reef 
on the seaward sides. Mixed seagrass com- 
munities (dominated by Thalassodendron 
ciliatum) and associated seaweeds cover 60 
percent of the lagoon, which Is typical for most of 
such lagoons along the Kenyan coast. Turbulent 
water motion (exposure) in these areas is relatively 
high compared with the sheltered creeks and bays 
and, due to hydrodynamic forcing, the spatial and 
temporal concentrations of nutrients and chloro- 
phyll a do not reach eutrophic levels because the 
lagoon is well flushed. 

Large banks of macrophytes, 88 percent of 
which is seagrass, are deposited on the beaches 
(beach cast] as the plants become detached from 
the sea bottom by the surge effect from waves. 
This phenomenon is seasonal and controlled by 
tides and monsoon winds'” “!. The most intense 
accumulations - as much as 1.2 million kg dry 
weight along a 9.5-km stretch of beach - are 
washed ashore during the southeast monsoons 
when wind and current speeds, water column 
mixing and wave height are usually greatest’. 

The Mombasa Marine Park is “fenced” by a 

to have a lower abundance of meio- and macrobenthos 
than unvegetated sandy areas, and may cause declining 
seagrass productivity due to shading’*°”!. 


Kenya has been one of the most active countries in 
marine conservation in Africa. The first marine 
protected area was gazetted as early as 1968. Kenya's 
guidelines for establishing parks and reserves, 
safeguarding marine ecosystems and preserving rare 
species have been adopted from the United Nations 
Environment Programme's (UNEP’s) Action Plan for 
the East African Regional Seas Programme". 

There are no existing management practices to 
protect existing seagrass beds from overexploitation or 
pollution per se. However, concern for the marine 
environment is demonstrated by the establishment of 
six marine protected areas covering a total area of 850 
km? while an additional marine reserve has been 
proposed. All protected areas are under the 


stretch of about 30 hotels, whose guests enjoy the 
white sandy beaches and other water sports 
within a stone's throw of their rooms. Although the 
beach cast phenomenon is seasonal and only 
peaks during the low season, the burgeoning 
tourism industry in this area considers it a 
nuisance and would prefer its removal. Some of 
the hotels employ staff to rake the seagrass 
material from the beach in the immediate vicinity 
of the hotel and bury it under the sand. A detailed 
study on the beach cast phenomenon showed that 
burying the material does not significantly affect 
decomposition rates’. 

The same study, however, also pointed to the 
role of seagrass beach cast in contributing to 
beach stability. By filtering out wave action, the 
beach cast material can reduce erosion of 
beaches caused by swash/backwash processes. 
The beach cast material may also reduce beach 
erosion due to wind. Furthermore, the cumulative 
effects of removing seagrass beach cast may 
intensify beach erosion either through the export 
of sand in the process or the loosening up of 
compact sand, or through removal of the 
protecting material that slows wave action. The 
potential rate of beach erosion in this study was 
estimated at 492450 kg of beach sand (per 
removal) if beach cast material at any given 

custodianship of the Kenya Wildlife Service, a well- 
equipped parastatal organization that has received 
much donor support. Most, if not all, of the marine 
protected areas in Kenya contain seagrass beds, but 
detailed distribution maps of seagrasses in these 
protected areas are not available. 

In addition, several legal and administrative 
instruments address aspects related to the protection 
and management of marine protected areas and thus 
(indirectly) of seagrass ecosystems. These include the 
protection of wildlife species, regulation of fisheries, 
land planning and coastal developments, research and 
tourism. Dugongs and turtles are both listed as 
“protected animals” under the Wildlife Conservation 
and Management Act and various initiatives for their 
conservation have been implemented. By working 
closely with respective local authorities, the Kenya 
Wildlife Service may avoid approval of activities that 
could impact negatively on marine parks, as provided 
for under the Land Planning (1968) and the Physical 

moment was removed from the entire beach (9.5- 
km stretch] 

The total annual deposition of seagrass 
beach cast was estimated to be in the order of 6.8 
million kg dry weight, indicating that about 19 
percent of the annual production of seagrass 
meadows [14.7 million kg carbon/year) in the 

lagoon passes through the beach, where 
decomposition is accelerated through exposure to 
oxygen availability, drying and vigorous 

fragmentation by wave action'”. These processes 
speed up the release of dissolved nutrients and 
particles back into the adjacent ecosystems and 
thus contribute to the detrital or energy pathways 
The material was further found to contain over 
23000 amphipods/m?, 3100 isopods/m? and 
various other faunal groups, providing an 
important food source for fishes during high tide 
The role of seagrass beach cast accumulations in 
nutrient regeneration processes and beach 
stability, and as nursery sites and a source of food 
for fish, crabs and shorebirds in the nearshore 
zone, is thus highly significant. Removing 
seagrass beach cast, though desirable for 
tourism, would have negative impacts on the 
health and functioning of adjacent seagrass beds, 
on which artisanal fisheries and tourism itself rely. 

Seagrass beach cast in Mombasa Marine National Park, 1995 - 
significant amounts of seagrass litter are washed up 
on the Kenyan beaches with each tide 

Planning [1996] Acts. Efforts are being made to 
encourage environmentally sensitive tourism as one of 
the measures to achieve protection goals. A draft 
national strategy for sea turtle conservation is currently 
under review while seagrasses have been considered in 
the most recent management plan of the Mombasa 
Marine National Park and Reserve. 

Outside marine protected areas, however, 
management and control over the exploitation of coastal 
and marine resources are virtually non-existent. 
Conservation of coastal and marine systems has 
concentrated its attention on either tourism-related or 
directly exploitable marine resources such as shells and 
coral reefs. Therefore it would seem that the important 
functions of seagrass beds related to fisheries nursery 
grounds, or to marine primary production, their 
contribution to energy pathways [involving a diversity of 
organisms], or linkages with land-based activities are 
not at the top of the conservation agenda. 

Since the recommendations to establish marine 

Kenya and Tanzania 

Photo: P.LA. Erftemeijer 


protected areas in Tanzania’”, the first two marine 
parks, of which seagrass ecosystems are part, were 
only recently gazetted in 1995. Despite considerable 
effort, the management of protected areas in Tanzania, 
as in many developing countries, suffers from 
insufficient capacity and law enforcement. One of the 
stated objectives of the National Fisheries Policy and 
Strategy, provided for by the Fisheries Act (1970), is to 
protect the productivity and biological diversity of 
coastal and aquatic ecosystems by preventing habitat 
destruction, pollution and overexploitation. 

Tanzania's Coastal Management Partnership, 
whose goal is to establish a foundation for effective 
coastal zone governance, has produced the first 
national programme for Integrated Coastal Manage- 
ment. Among the first outputs of this program are a 
State of the Coast Report, a National Mariculture Issue 
Profile, guidelines and a conflict resolution forum 
dealing with such issues as trawling and dynamite 
fishing. A draft national Integrated Coastal Manage- 



ment Strategy is awaiting government approval. These 
initiatives and, more so, the process have raised the 
profile and level of understanding of the importance of 
coastal and marine resources, including seagrass 
beds. Implementation of integrated coastal zone 
management initiatives in Tanzania is currently under 
way in Tanga (by IUCN-The World Conservation Union), 
Zanzibar (Menai Bay Conservation Project], Mafia 


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& VR 

8 The seagrasses of 

Mozambique and southeastern Africa 


and 12 in the remaining southeastern African 

region. Madagascar has nine common species. 
Five species occur in South Africa, seven in Mauritius 
and up to ten in Comoros and Seychelles!" **. Ruppia 
maritima, recently defined as a seagrass, is also a 
dominant species in the southeastern Africa region. 

[oe seagrass species occur in Mozambique 



The Mozambican coast can be divided into three 
regions: a sandy coastline from the southern end of the 
country to the Save River; an estuarine coastline from 
the Save River up to around 500 km north of the 
Zambezi River; and a rocky limestone coastline, 
typically surrounded by coral reefs, which runs from 
the Zambezia province up to the northern end of the 
country, and also covers the Tanzanian and Kenyan 
coasts’). Seagrasses abound in the sandy and 
limestone areas. 

Seagrasses in general occur in mixed seagrass 
stands, especially in intertidal areas. The three 
dominant mixed-seagrass communities on the sandy 
substrates of southern Mozambique consist of 
combinations of Thalassia hemprichii, Halodule 
wrightii, Zostera capensis, Thalassodendron ciliatum 
and Cymodocea serrulata”’. 

In contrast, the seagrass communities of the 
more northerly limestone areas are quite different, with 
seagrasses tending to occur intermingled with 
seaweed species”. Here, the dominant botanical 
communities also include Thalassia hemprichii and 
Halodule wrightii, but species such as Gracilaria 
salicornia, Halimeda spp. and Laurencia papillosa 
occur mixed with Thalassia hemprichii, and Sargassum 
spp. with Thalassodendron ciliatum. Elsewhere 
Zostera capensis and Halodule wrightii also form 
mixed beds. 

In general Thalassodendron ciliatum and 

S.0. Bandeira 
F. Gell 

Thalassia hemprichii are the dominant subtidal sea- 
grass species in Mozambique. A detailed comparison 
has been made of the former growing along the rocky 
and sandy coasts of southern Mozambique”. Leaves 
appear to grow faster on plants in the rocky areas (20- 
26 g/m’/day and up to 57 mm/‘/day) than in sandy (8-10 
g/m*/day and up to 22 mm’/day). Leaf biomass in rocky 
areas is more than twice that of sandy (258 g/m? and 
124 g/m’ respectively) and beds are characterized by a 
much higher shoot density (4561 shoots/m* and 888 
shoots/m* respectively). 

The underground biomass of Thalassodendron 
ciliatum is presumably relatively high in sandy 
environments because total biomass (862 g/m’], while 
significantly lower than in the rocky seagrass beds 
(1070 g/m}, is comparable. Although possibly slower 
growing, the Thalassodendron ciliatum plants in the 
sandy habitat have wider (1.4 cm +0.1) and longer 
(12.51 cm +0.6) leaves than in the rocky habitat (0.7 cm 
+0.1 and 8.2 +0.5 respectively). The biomass of 
epiphytes on Thalassodendron ciliatum plants is an 
order of magnitude higher in the rock (512 g/m’) than in 
the sand (40 g/m’), and consequently these organisms 
account for nearly half (48 percent) of the combined 
seagrass and epiphyte biomass, compared with just 5 
percent in the southern sandy-bottom beds. 

Enhalus acoroides, Halophila stipulacea and 
Halophila minor are found only in northern 
Mozambique while pure stands of Zostera capensis are 
found only in the south”. Pioneer species observed in 
Mozambique include Halodule wrightii, Halophila 
ovalis and Cymodocea serrulata. The first two species 
act as pioneers in exposed sandy areas close to the 
coastline, whereas Cymodocea serrulata is a pioneer in 
silted channels. 

South Africa 
Zostera capensis is most widespread and one of the 
dominant seagrass species in South Africa. It occurs 


* Quirimba Archipelagd O° S) 
re - 

MOZAMBIQUE, Montepuc= Bay 

Fernao . 
Lum Veloso J 

‘ Goa 




Bazaruto | 
Inhambane Bay 

Maputo Bay. «®% 
Ne Xai-Xai 

of Inhaca Island 

® Kwazulu-Natal 


0 200 400 600 800 1000 Kilometers 

Map 8.1 
Mozambique and southeastern Africa 



La Digue 

SiJhouette Seychelles Bank 

e Anse aux Pins 


45 Kilometers 

Map 8.2 
The Seychelles 

® Poudre d'Or 

Poste Lafayette 



10 15 20 25 Kilometers 
98° E 

Map 8.3 

Table 8.1 

Area cover and location for the seagrass Zostera capensis in 

South Africa 


St Lucia 
Krom Oos 



Warm temperate 
Warm temperate 
Warm temperate 
Warm temperate 
Warm temperate 
Warm temperate 
Warm temperate 
Warm temperate 
Warm temperate 
Warm temperate 
Warm temperate 

Estuarine lake 
Permanently open 
Permanently open 
Permanently open 
Permanently open 
Permanently open 
Estuarine bay 
Estuarine lake 
Estuarine lake 
Permanently open 
Permanently open 
Permanently open 
Permanently open 
Permanently open 
Temporarily closed 
Temporarily closed 
Temporarily closed 

Total 7.07 


Source: Colloty 

mostly in estuarine waters along a number of estuaries 
from Kwazulu-Natal to the western Cape region. 

Another important location with seagrass 
species is found off Kwazulu-Natal. Here, a number of 
rocky protuberances into the sea are mostly 
dominated by Thalassodendron ciliatum adapted to 
live in rocky habitat together with seaweeds". These 
rocky areas generally experience strong water 
dynamics and winds similar to those of southern 

The distribution of Zostera capensis in southeast 
South Africa is well recorded. It grows in 17 estuaries 
(Table 8.1]. Individual beds are small, generally only a 
few hectares, and the total area covered by seagrass is 
about 7 km’. 


Little is known about the relative dominance 
of seagrass species in Madagascar although it is 
likely that in the southwest of the country they are 
similar to the species from the limestone areas of 
Mozambique, with most of the meadows being domin- 
ated by Thalassodendron ciliatum and Thalassia 
hemprichii. Seaweeds are also a common feature in 
the intertidal and subtidal seagrass areas of 


Thalassodendron ciliatum, Halodule uninervis and 
Syringodium isoetifolium appear to be the most 
common seagrass species in Mauritius’. 


Little is known about the seagrass meadows of 
Comoros. Being located less than 400 km east of the 
coastline of Mozambique and sharing a similar climate, 
Comoros may have similar meadows to northern 
Mozambique with mixed seagrass species in intertidal 
areas and subtidal seagrass species dominated by 
broad-leaved species such as Thalassodendron 


Seychelles is composed of 115 granite and coral 
islands. Seagrass meadows are dominated by 
Cymodocea serrulata. Syringodium isoetifolium and 
Thalassia hemprichii occur at Anse aux Pins”! on the 
main island of Mahé. Shoot density varies from 1093 to 
1107 shoots/m’ in Cymodocea serrulata plants, 1123 to 
1761 in Syringodium isoetifolium and 540 to 627 in 
Thalassia hemprichii*. Thalassodendron ciliatum is 
also common in subtidal areas down to depths of 33 m 
throughout the Seychelles!” 


The Quirimba Archipelago is a chain of 32 islands off 
the coast of northern Mozambique, running from north 
of the town of Pemba up to the Tanzanian border. One of 
the largest and most populated islands in the chain is 
Quirimba. Quirimba is 6 km long by 2 km wide and has 
a population of 3000. This island is separated from the 
mainland by the Montepuez Bay. The island’s main 
fishery is located in the shallow seagrass beds of the 
bay, and this seagrass fishery is the main source of 
income and protein for people on the island. In 1996 
and 1997 part of the Darwin/Frontier Quirimba 
Archipelago Marine Research Programme studied the 
Quirimba fishery which is dependent on a diverse 
seagrass ecosystem!" 

Montepuez Bay is between 1 and 10 m deep and 
has extensive intertidal flats and banks, large areas of 
which are covered in seagrass. The bay takes its name 
from the Montepuez River, which enters the southwest 
of the bay from the Mozambique mainland. Ten species 
of seagrass are present in the bay: Enhalus acoroides, 
Thalassodendron ciliatum, Cymodocea rotundata, 
Cymodocea serrulata, Syringodium isoetifolium, 
Halodule uninervis, Halodule wrightii, Halophila ovalis, 
Halophila stipulacea and Thalassia hemprichii. 

The intertidal seagrass beds are dominated by 
Thalassia hemprichii. Subtidally, the most abundant 
species are Enhalus acoroides and Thalassodendron 

Mozambique and southeastern Africa 

ciliatum, both of which can grow to over 1 m in height, 
and the smaller species Cymodocea rotundata and 
Cymodocea serrulata. Small seagrass species (e.g. 
Syringodium isoetifolium, Halophila spp. and 
Halodule spp.) are present in small quantities, often 
forming an understorey in stands of larger species. In 
quadrat surveys of the Montepuez Bay seagrass beds, 
the most common seagrass types were stands 
dominated by Enhalus acoroides. The most common 
combination of seagrasses found was Enhalus 
acoroides with Halophila ovalis, which were mainly 
found together in areas that were exposed to the air at 
very low tides. 

Such a predominance of Enhalus acoroides is 
unusual in the region and, even within the Quirimba 
Archipelago which has extensive seagrass beds, 
Montepuez Bay was the only area dominated by 
Enhalus acoroides. Other subtidal seagrass beds in the 
Quirimba Archipelago were dominated by Thalasso- 
dendron ciliatum. Dense meadows of tall [often 
between 50 and 100 cm) Enhalus acoroides were home 
to a diverse range of invertebrates and fish, and the 
seagrass itself was covered in epiphytes, altogether 
constituting a complex habitat. Over 30 species of algae 
were identified living on or in association with the 
seagrass'”. Fishers in Montepuez Bay target shallow 
areas of Enhalus acoroides for their main fishing 
activities, whilst women collect invertebrates in the 
intertidal seagrass beds dominated by Thalassia 
hemprichii. Although the direct use of seagrass plants 
has been reported from other places, this was not 
observed in the Quirimba Archipelago. 

Fishing methods 

Seine nets were set from small sail-powered boats by 
teams of between five and 12 men. Fishermen in the 
water kept the net in place and drove the fish into the net 
as it was hauled into the boat. Seine net fishing was 
carried out in shallow water, from 1 to 8 meters deep, in 
areas of Enhalus acoroides. The nets used were 
approximately 100 m in length with a main mesh size of 
4 cm stretch and a cod-end of 2 cm stretch, or less. The 
mean duration of a fishing trip was about five hours and 
the mean catch per trip was 75 kg. Catch per unit effort 
was 3.6 kg of fish per man-hour spent fishing or 2 kg of 
fish per man-hour spent at sea. The net catches were 
highly diverse, with a total of 249 fish species in 62 
families identified from more than 46 600 fish sampled’. 
The fishers also caught invertebrates in the seine nets, 
particularly squid. Approximately 30 fish species were 
common in the catch. The most important species in the 
net fishery in terms of weight were the African 
whitespotted rabbitfish Siganus sutor (24 percent); the 
pink ear emperor Lethrinus lentjan (12.2 percent); the 
seagrass parrotfish Leptoscarus vaigiensis (11 percent); 






A marema fish trap in an Enhalus acoroides bed, Mozambique 

the variegated emperor Lethrinus variegatus (7.4 
percent); the blacktip mojarra Gerres oyena (6.3 percent] 
and the spinytooth parrotfish Calotomus spinidens (3.2 
percent). The majority of fish caught in seine nets were 

Case Study 8.1 

Seagrasses at Inhaca Island and Maputo Bay area 
cover more than 80 km’. At Inhaca Island the 
seagrasses alone cover around 50 percent of the 
entire intertidal area”. The diversity of seagrasses is 
very high, especially at Inhaca Island where eight 
seagrasses species can be found in just one 
hectare”. Nine seagrass species have been 
identified in the area namely: Cymodocea rotundata, 
Cymodocea serrulata, Halodule uninervis, Halodule 
wrightii, Halophila ovalis, Syringodium isoetifolium, 
Thalassia hemprichii, Thalassodendron ciliatum and 
Zostera capensis”. These seagrass species are 
grouped in three main dominant seagrass com- 
munities: Thalassodendron ciliatum/Cymodocea 
serrulata, Thalassia hemprichli/Halodule wrightii 
and Zostera capensis”™'. Zostera capensis shoot 
density is higher at Inhaca (2880 shoots/m/) than at 
Maputo Bay [1285 shoots/m’) as are leaf, rhizome 
and root biomass?” 

The species Thalassia hemprichii and 
Thalassodendron ciliatum tend to occupy deeper 
areas far from the coastline whereas Halodule 
wrightii and Cymodocea serrulata tend to occupy 
shallow areas closer in. Thalassodendron ciliatum, 

less than 15 cm long and many were juveniles. Virtually 
all the fish caught in the seine net fishery were eaten. 
Amongst the more unusual food species that were 
common in the fishery were the tailspot goby 
Amblygobius albimaculatus and the three-ribbon 
wrasse Stethojulis strigiventer. 

The traps used in Montepuez Bay are known 
locally as marema. They are of an arrowhead design 
and constructed from woven bamboo panels secured 
together with palm fibers. Marema were set by 
fishermen from outrigger canoes in shallow areas of 
Enhalus acoroides at low tide, and were hauled the 
following day at low tide. The traps were sometimes 
baited with crushed TJerebralia snails collected from 
mangrove areas, or with squid, but often the traps were 
not baited at all. The traps were weighed down with 
stones and placed amongst long, densely growing 
Enhalus acoroides (the fishermen said that this 
seagrass was very important for keeping the traps in 
place in the strong tidal currents]. The mean daily catch 
for a fisherman setting 40 traps was nearly 7 kg of fish, 
although catches could be as high as 27 kg per trip. 
The catch per unit effort for the trap fishery was 2.2 kg 
of fish per hour spent fishing and the mean catch for a 
trap set for 24 hours was 0.2 kg of fish. Trap catches 


in the subtidal fringe, occurs in homogeneous stands 
except in some areas where it is also accompanied 
by a band of Syringodium isoetifolium parallel to the 
coastline. When Thalassia hemprichii and Halodule 
wrightii co-occur in mixed species communities, 
Thalassia hemprichii is found in small depressions 
whereas Halodule wrightii occupies elevated areas 
which are exposed at low spring tides. 

Seagrass meadows in Maputo Bay region are 
widely used by the people who collect, by hand, 
seafood from them, the most common being 
mussels {Anadara natalensis, Cardium flavum, 
Modiolus phillipinarum), oysters (Pinctada capensis), 
gastropods (Conus betulinus, Strombus gibberulus) 
and sea urchins le.g. Salmacis bicolores, 
Tripneustes gratilla). They also use the meadows for 
fishing using traditional techniques, for species such 
as Crenidens crenidens, Gerres  acinaces, 
Leiognathus equulus, Lithognathus aureti, Liza 
macrolepis, Lutjanus fulviflamma, Platycephalus 
indicus, Pseudorhombus arsius, Rhabdosargus 
sarba, Scarus ghobban, Siganus sutor and Terapon 
Jarbua, and crustaceans such as Matuta lunaris and 
Portunus pelagicus®*“*!. The sea cucumber 

were dominated by the parrotfish Leptoscarus 
vaigiensis, which accounted for over 74 percent of the 
fish caught by weight. Other important species included 
the parrotfish Calotomus spinidens (5 percent by 
weight], the rabbitfish Siganus sutor (4 percent), the 
dash-dot goatfish Parupeneus barberinus (4 percent), 
the blackspot snapper Lutjanus fulviflamma (3 percent] 
and the flagfin wrasse Pteragogus flagellifera (2.5 
percent]. A total of 61 species of fish were identified 
from 3500 fish sampled from the trap fishery, with 
about 16 of these species appearing commonly in the 
fishery. A wide variety of invertebrates entered the 
traps, including swimming crabs (Portunidae) which 
were kept for use as food. 

Spatially referenced catch data from the seine net 
fishery was used to identify the fishing sites in 
Montepuez Bay with the highest mean fish catch per 
unit effort. These were also the sites with the highest 
mean percentage cover of seagrass and highest 
seagrass biomass. This suggests that seagrass cover 
and biomass may influence fish biomass and fishery 
productivity. In experimental trap fishing, the prefer- 
ence of trap fishermen for areas of Enhalus acoroides 
to other species of seagrass was shown to be well 
founded. In these experiments the mean catch per trap 

Holothuria scabra, presently endangered in many 
parts of the country, was earlier heavily collected by 
the local people at Inhaca and north of Maputo city 
and sold for export to Asia. The same is true of 
Holothuria atra, but to a lesser extent. 

More than 20 nets are set daily around Inhaca 
Island from boats and by people walking on the 
beach, and around 100 people may be seen collecting 
edible organisms during the spring low tides”. To the 
north of Maputo city, at the fishing village of Bairro 
dos Pescadores, close to 50 people dug up seagrass 
meadows at spring low tide for collection of 
invertebrates, mainly bivalves, in the mid-1990s". 
Recent counting estimated around 200 people 
involved in this activity, which includes digging the 
intertidal areas for the same purpose. Seagrasses 
have also been reported as being used for alluring 
and bewitching at Inhaca Island” and the dried 
detached leaves of Thalassodendron ciliatum as 
being used to fill pillows. 

The seagrasses of the area are under consider- 
able stress from a variety of sources. Sewage 
disposal along the Maputo coastline threatens sea- 
grasses there, with polluted areas tending to be 
covered by seaweeds Ulva spp. and Enteromorpha 
spp. instead of seagrass. Additional pollution, 
especially oil spills, comes from the city harbor and 

Mozambique and southeastern Africa 

for Enhalus acoroides greatly exceeded that for other 
common seagrass species, Thalassodendron ciliatum 
or Cymodocea spp. Catch compositions from the three 
different seagrass species were also different. Catches 
from Enhalus acoroides beds were dominated by the 
parrotfish Leptoscarus vaigiensis as the fishermen’s 
catches were, but catches from Thalassodendron 
ciliatum beds were dominated by the file fish 
Paramonacanthus barnardi, and catches from 
Cymodocea spp. by the snapper Lutjanus fulviflamma. 

Invertebrate fishery 

Women did most of the collecting of seagrass inver- 
tebrates that could be achieved without a boat. They 
walked out over the seagrass beds at low tides and 
collected bivalves by hand. On spring tides, some women 
traveled in groups by boat to some of the larger banks in 
the bay that become exposed at low tide. 
The main species they collected were the ark shell 
Barbatia fusca and the pinna shell Pinna muricata, found 
in sand in seagrass beds, and the oyster Pinctada nigra 
which grows on the seagrass plant itself. These shellfish 
were dried and most of them were sold on the mainland 
for higher prices than they would fetch on the island, 
particularly the pinna shell which is a local delicacy”. 

industrial area. Sedimentation due to erosion and 
floods further diminishes local seagrass coverage 
around Maputo. Trampling and the heavy concen- 
tration of fishing and tourist activities directly disturb 
seagrass meadows at Inhaca Island's main village. 
Fishing in very shallow water is another disturbance. 
The combination of all these factors places heavy 
pressures on the extensive seagrass meadows, and 
has already caused a disappearance of Zostera 
capensis from in front of Inhaca’s main village”. 
Some priority areas for intervention to reduce 
these disturbances include increased monitoring 
and reduction of sewage disposal, industrial pollu- 
tants and port activities. At Inhaca Island, only the 
seagrass beds located close to coral reefs are under 
protection. This protection should be reviewed to 
target the conservation of seagrass areas with a high 
concentration of threatened and depleted in- 
vertebrate species such as holothurians and 
seastars, e.g. Holothuria scabra and Holothuria atra. 
The Thalassodendron ciliatum communities occur- 
ring in rocky protuberances in the sea habitats have 
only recently been described. This form of seagrass 
only occurs in sandstone rocks facing the strong 
waves of the Indian Ocean"! Few similar areas exist 
in Mozambique and therefore some kind of pro- 
tection should be put in place for their conservation. 





Some fishermen went out on the seagrass beds 
in small canoes to dive with a mask to collect 
invertebrates, mainly sea cucumbers, and mollusks 
such as the tulip shell Pleuroploca trapezium and the 
murex Chicoreus ramosus. Sea cucumbers were one 
of the more valuable seagrass residents and were 
dried and sold across the border in Tanzania, to be 
exported to markets in the Far East. During the study 
period fishermen reported the virtual disappearance 
of sea cucumbers from the seagrass beds of 
Montepuez Bay, and attributed this to overexploitation 
by local and itinerant fishers. Fishermen involved in 
the seine net and trap fishery would also collect 
murex, tulip shells and sea cucumbers when they got 
the opportunity. Tulip shells were collected for their 
opercula which were sold to traders in Tanzania. 
Murex were eaten and the shells of these and other 
mollusks were collected and burnt for lime that was 
used locally in building. 

Subtidal surveys identified 34 species of large 
invertebrates which were associated with the seagrass 
beds. Commonly observed invertebrates that were not 
collected locally included the sea urchins Diadema 
setosum and Tripneustes gratilla, the sea cucumber 
Synapta maculata and the starfish Pentaceraster 
tuberculatus and Protoreaster lincki. 

Local value of seagrass resources 
The seagrass fisheries of Montepuez Bay supported 
over 400 fishermen on Quirimba Island alone and many 
more in the mainland villages and from other islands in 
the vicinity. More than a hundred women from Quirimba 
also collected invertebrates in the seagrass beds. In 
total over 500 people were involved in the seagrass 
fisheries of Quirimba, out of a total population of 3000. 
The total fish catch from the 35 km? seagrass beds of 
the whole bay was estimated at around 500 metric tons 
per year, or 14.3 metric tons per km* per year. 
This figure does not include invertebrates, but is still 
high compared with many tropical reef and estuarine 
fisheries. A minimum estimate for annual invertebrate 
collection from seagrass beds around Quirimba was 40 
metric tons per year. 

In the study period, the fish caught in Montepuez 
Bay had an estimated annual saleable value of ca 
US$120000, based on prices paid for fish locally. Roughly 
half the fish caught was consumed by the fishers and 
their families or exchanged for other goods or services. 
The other half was dried and traded on the mainland by 
the owners of the net fishing boats, or other traders who 
buy the surplus from trap fishermen. 

Management issues 
During the study period the local fishery seemed to 
have a relatively low impact on the seagrass beds and 

was apparently sustainable. The seine net fishery did 
appear to have some negative effects on the seagrass 
beds. The nets were often dragged along the bottom 
and substantial amounts of seagrass, sponges and 
small corals were sometimes brought up with the nets. 
Trampling of intertidal seagrass was kept to a 
minimum by the use of small paths across the 
seagrass that restricted the trampling damage to a 
small area. The main threats to the sustainability of the 
seagrass fishery came from external sources, mainly 
unregulated itinerant fishers and commercial sea 
cucumber fishing for international trade. On a larger 
scale, potential threats came from upstream activities 
in the catchment of the Montepuez River - particularly 
deforestation leading to changes in sedimentation 

With so many people relying on the seagrass beds 
of Montepuez Bay for their livelihoods, and with the 
paucity of alternative employment or sources of 
protein, their conservation and sustainable use is vital. 
One of the reasons that the resources of the Montepuez 
Bay seagrass beds are so widely used is that the habitat 
is so accessible, even to those with the most limited 
resources. Much of the seagrass can be reached on foot 
at low tide, and even the deeper areas are close to 
shore and are sheltered from the heavy seas that the 
eastern coast of the island is subject to. At the time of 
this study Quirimba Island had rich and diverse marine 
resources including mangrove forests and extensive 
coral reefs on the east coast. However, few fishers 
utilized the reef resources because of the difficulties of 
accessing the exposed reefs in their traditional fishing 
vessels. This issue of the accessibility of seagrass beds 
is seen in other places where fishers with small boats, 
or on foot, are able to fish in seagrass beds in shallow 
sheltered bays or lagoons. A priority for seagrass 
research should be to look at how best to manage 
open-access, multi-user seagrass systems such as 
Montepuez Bay, to ensure their sustainable use, and to 
conserve biodiversity. The Quirimba Island seagrass 
fishery is a clear, and rare, example of the direct value 
of seagrasses to local communities. 


The digging of Zostera capensis beds to collect bivalves 
has dramatically depleted the seagrass cover at Bairro 
dos Pescadores {near Maputo, Mozambique] from a 
cover of around 60 percent or more to 10 percent or 
less in the last ten years (Figure 8.1]. This activity lasts 
for the entire spring tide period spanning about 15 days 
each month. The bivalves are collected mainly for food. 
It is expected that this activity will eventually 
completely destroy the Zostera capensis beds at Bairro 
dos Pescadores, and that the food security of the local 
population will suffer as a consequence. 

Photos: S.0. Bandeira 

Sedimentation due to floods has buried sea- 
grasses in Maputo Bay and Inhassoro. In the heavy 
floods in southern Mozambique in 2000 around 24 km’ 
of seagrasses may have been buried here. Harbor 
development, sewage and coastal development in 
areas of southern Mozambique have further diminished 
seagrass coverage. Heavy concentrations of artisanal 
fishing boats in combination with intense trampling in 
low tides have also caused reduction of seagrass 
species at Inhaca Island. 

In Mauritius seagrasses are threatened by the 

Figure 8.1 
Digging of Zostera capensis meadows at Vila dos Pescadores, near 
Maputo city 

a. Photo taken in 1994 - hunks of plants being lifted, washed an: 
then placed upside down - plant cover is still high. 

b. Photo taken in 2002 - plant cover is very low and in most areas 
the seagrass has already disappeared. 

Mozambique and southeastern Africa 

high use of fertilizers in the sugar cane industry, and 
specifically by the eutrophication of coastal lagoons 
that is caused when they leach into these shallow 
contained areas. Seagrass beds are being dredged 
and destroyed to provide bathing and skiing areas for 
tourists. Sedimentation, sewage disposal and sand 
mining are among other threats to Mauritius 

In Anse aux Pins, Seychelles, sedimentation, 

Table 8.2 
Seagrass cover and area lost in Mozambique 

Site name Main seagrass Area Area lost 
species (km) {km’} 
Quirimba Cr, Cs, Ea, Hm, 45 
Archipelago Ho, Hs, Hw, Tc, Th 
Mecufi-Pemba Hm, Ho, Hs, Hu, 30 
Hw, Si, Tc, Th, Zc 
Fernao Veloso Cr, Cs, Ea, Hm, 
Ho, Hu, Hw, Si, 
Tc, Th 
Quissimajulo Th 
Relanzapo Tc, Th, 
Matibane- Cr, Hw, Tc, Th 
Chocas Mar- 
Cabaceira Grande- 
Sete Paus Island 
Mozambique Cr, Cs, Hm, Ho, 
Istand-Lumbo- Hu, Hw, Si, 
Cabaceira Pequena Tc, Th, Zc 
Goa Island Tc 
Inhassoro- Cs, Tc, Th 
Bazaruto Island 
Inhambane Bay Hw 
Xai-Xai Tc, macroalgae 
Bilene Rm, Hu 
Maputo Bay Ho, Hw, Tc, Th, Zc 
Inhaca Island Cr, Cs, Ho, Hu, 
Hw, Si, Te, Th, Zc 
Inhaca-Ponta Tc, macroalgae 
do Ouro 
Total 439.04 27.55 

Notes: Cr Cymodocea rotundata; Cs Cymodocea serrulata; 
Ea Enhalus acoroides; Hm Halophila minor; Ho Halophila ovalis; 
Hs Halophila stipulacea; Hu Halodule uninervis; Hw Halodule 

wrighti; Rm Ruppia maritima; Si Syringodium isoetifolium; 
Tc Thalassodendron ciliatum; Th Thalassia hemprichii; 
Zc Zostera capensis. 




salinity and decreased water quality associated with a 
river effluent discharge have adversely affected 

seagrasses". Flooding in estuaries is the main threat to 

the survival of Zostera capensis on the South African 
east coast. 

Other areas where seagrass cover has been lost 
include Pemba, Mozambique Island, Inhambane Bay 
and Inhaca Island (Table 8.2). The total known historical 
loss of seagrasses in Mozambique is 27.55 km’, 
although some of the areas affected by the 2000 floods 
have already regained seagrass cover. 

In Mauritius, seagrasses have diminished from 
areas such as Albion (Halodule uninervis), Poudre 
d'Or, Mont Choisy and Poste Lafayette (Syringodium 
isoetifolium) though the actual area lost is unknown. 
Similarly areas covered by Zostera capensis in 
estuaries in Kwazulu-Natal, South Africa, are believed 
to have been seriously depleted by periodic heavy 
floods"! without measurements being available. 
Nothing is known about the loss of seagrass from 
Madagascar, Comoros or Seychelles. 


1 Titlyanov E, Cherbadgy |, Kolmakov P [1995]. Daily variations of 
primary production and dependence of photosynthesis on 
irradiance in seaweeds and seagrass Thalassodendron ciliatum of 
the Seychelles Islands. Photosynthetica 31: 101-115. 

2 Bandeira SO (2000). Diversity and Ecology of Seagrasses in 
Mozambique: Emphasis on Thalassodendron Ciliatum Structure, 
Dynamics, Nutrients and Genetic Variability. PhD thesis, Goteborg 

3 Ingram JC, Dawson TP [2001]. The impacts of a river effluent on a 
coastal seagrass habitat of Mahe, Seychelles. South African 
Journal of Botany 67: 483-487. 

4 Short FT, Coles RG, Pergent-Martini C [2001]. Global seagrass 
distribution. In: Short FT, Coles RG [eds] Seagrass Research 
Methods. Elsevier Publishing, Amsterdam. pp 5-30. 

5 Hartnoll RG [1976]. The ecology of some rocky shores in tropical 
East Africa. Estuaries Coastal Marine Science 4: 1-21. 

6 Gove DZ [1995]. The coastal zone of Mozambique. In: Lindén 0 (ed) 
Workshop and Policy Conference on Integrated Coastal Zone 
Management in Eastern Africa including the Island States. 
Conference Proceedings. Coastal Management Center (CMC), 
Metro Manila. pp 251-273. 

7 Bandeira SO [1995]. Marine botanical communities in southern 
Mozambique: Sea grass and seaweed diversity and conservation. 
Ambio 24: 506-509. 

8 Bandeira SO, Antonio CM [1996]. The intertidal distribution of 
seagrasses and seaweeds at Mecufi Bay, northern Mozambique. In: 
Kuo J, Phillips RC, Walker DI, Kirkman H (eds) Seagrass Biology: 
Proceedings of an International Workshop. University of Western 
Australia, Nedlands. pp 15-20. 

9 Bandeira SO [2002]. Leaf production rates Thalassodendron 
ciliatum from rocky and sandy habitats. Aquatic Botany 72: 13-24. 

10 Bandeira SO, Bjork M [2001]. Seagrass research in the eastern 
Africa region: Emphasis to diversity, ecology and ecophysiology. 
South African Journal of Botany 67: 420-425. 

11 Barnabas AD [1991]. Thalassodendron ciliatum (Forsk.) den 
Hartog: Root structure and histochemistry in relation to apoplastic 
transport. Aquatic Botany 40: 129-143. 


Mozambique has a total of 439 km’ of seagrasses (Table 
8.2]. There are 25 km? around Inhassoro and Bazaruto 
Island, 30 km? at Mectifi-Pemba and 45 km’ in the 
southern Quirimba Archipelago. The largest seagrass 
beds occur at Fernao Veloso, Quirimba and Inhaca- 
Ponta do Ouro. Additional inventories are needed, 
particularly in remote coastal areas. In South Africa 
Zostera capensis covers a total area of just over 7 km’: 
other seagrasses species cover smaller areas. While 
extensive seagrass meadows do occur in Madagascar, 
Mauritius, Comoros and Seychelles, the exact area is 


Salomao 0. Bandeira, Department of Biological Sciences, Universidade 
Eduardo Mondlane, P.0. Box 257, Maputo, Mozambique. Tel: +258 (0}1 
491223. Fax: +258 (0)1 492176. E-mail: sband( 

Fiona Gell, Environment Department, University of York, Heslington, York 
Y010 5DD, UK. 

12 Colloty BM [2000]. Botanical Importance of Estuaries of the Former 
Ciskei/Transkei Region. PhD thesis, University of Port Elizabeth. 202 pp. 

13 Rabesandratana RN [1996]. Ecological distribution of seaweeds in 

two fringing coral reefs at Toliara (SW of Madagascar). In: Bjork M, 

Semesi AK, Pedersen M, Bergman B [eds] Current Trends in 

Marine Botanical Research in East African Region. SIDA/SAREC, 

Uppsala. pp 141-161. 

Dulymamode. Personal communication. 

Parnik T, Bil K, Kolmakov P, Titlyanov E [1992]. Photosynthesis of 

the seagrass Thalassodendron ciliatum: Leaf anatomy and carbon 

metabolism. Photosynthetica 26: 213-223. 

Gell FR [1999]. Fish and Fisheries in the Seagrass Beds of the 

Quirimba Archipelago, Northern Mozambique. PhD thesis, 

University of York. 

Whittington MW, Antonio CM, Corrie A, Gell FR [1997]. Technical 

Report 3: Central Islands Group - lbo. 

Antonio MC. Unpublished data. 

Gell FR, Whittington MW [2000]. Diversity of fishes in seagrass beds 

in the Quirimba Archipelago, northern Mozambique. Marine and 

Freshwater Research 53: 115-121. 

20 Barnes DKA, Corrie A, Whittington M, Carvalho MA, Gell FR [1998]. 
Coastal shellfish resources use in the Quirimba Archipelago, 
Mozambique. Journal of Shellfish Research 17(1}: 51-58. 

21 Adams JB, Bate GC, O'Callaghan M [1999]. Estuarine primary 
producers. In: Allanson BR, Baird D [eds] Estuaries of South Africa. 
Cambridge University Press, Cambridge. pp 91-118. 

22 Martins ARO, Bandeira, SO [2001]. Biomass and leaf nutrients of 
Thalassia hemprichii at Inhaca island, Mozambique. South African 
Journal of Botany 67: 439-442. 

23 Martins AR [1997]. Distribuicdo, estrutura, dinamica da erva 
marinha Zostera capensis e estudo de alguns parametros fisicos 
em duas areas da Baia de Maputo. Licenciatura thesis, Eduardo 
Mondlane University, Maputo. 49 pp. 

24 Kalk M [1995]. A Natural History of Inhaca Island, Mozambique. 
Witwatersrand University Press, Johannesburg. 395 pp. 

25 de Boer WF, Longomane FA [1996]. The exploitation of intertidal 
food resources at Inhaca bay, Mozambique by shorebirds and 
humans. Biological Conservation 78: 295-303. 






9 The seagrasses of 


ndia has coastal wetlands of ca 63 630 km’, mostly 

consisting of estuaries, bays, lagoons, brackish 

waters, lakes and salt pans'’. The intertidal and 
supralittoral shallow sheltered regions of these wet- 
lands harbor various marine macrophytic ecosystems 
such as seaweed, seagrass, mangrove and other obli- 
gate halophytes. Coastal wetland habitats are of a 
productive nature, and are of immense ecological and 
socioeconomic importance. Marine macrophytes sup- 
port various kinds of biota, and produce a considerable 
amount of organic matter, a major energy source in the 
coastal marine food web; they play a significant role in 
nutrient regeneration and shore stabilization processes. 

The major seagrass meadows in India exist along 
the southeast coast (Gulf of Mannar and Palk Bay) and 
in the lagoons of islands from Lakshadweep in the 
Arabian Sea to Andaman and Nicobar in the Bay of 
Bengal (Table 9.1]. The flora comprises 14 species and 
is dominated by Cymodocea rotundata, Cymodocea 
serrulata, Thalassia hemprichii, Halodule uninervis, 
Halodule pinifolia, Halophila beccarii, Halophila ovata 
and Halophila ovalis (Table 9.2). Distribution occurs 
from the intertidal zone to a maximum depth of ca 
15 m. Maximum growth and biomass occur in the lower 
littoral zone to a depth of 2-2.5 m. Greatest species 
richness and biomass of seagrass occur mainly in open 
marine sandy habitats. 

Seagrasses, though one of a predominant and 
specialized group of marine flora, are poorly known in 
India, compared to other similar ecosystems such as 
mangroves. Earlier studies dealt mainly with the 
distributional and taxonomic aspects of Indian 
seagrasses”. Over the last 20 years, efforts have been 
made to understand the community structure and 
function of seagrass ecosystems in India“. However, 
the structure and function of Indian seagrass 
ecosystems remain poorly understood'*'”. Inadequate 
information and almost total lack of awareness might 
be the reasons for this lack of knowledge in India. 


T.G. Jagtap 
D.S. Komarpant 
R. Rodrigues 

Surprisingly, seagrasses have not been introduced 
even at the level of plant science education programs. 
Hence, large number of students, researchers and 
coastal zone managers in India may be unaware of the 
existence of seagrass ecosystems. Here, we present an 
overall account of seagrass habitats from India. 

Epiphytes form an important constituent of 
seagrass ecosystems in India, though very limited 
information is available”'". The floral epiphytes 
comprise a few species of marine algae belonging to 
Cyanophyceae, Chlorophyceae, Rhodophyceae and 
Bacillariophyceae. The Rhodophyceae, particularly 
Melobesia sp., occur frequently and are a dominant 
part of epiphytic biomass” ". Cyanophycean members 
such as species of Microcoleus, Mastogocoleus and 
Oscillatoria were observed to be dominant epiphytes. 
Ten species of diatoms have been reported on seagrass 
blades and roots. The oldest leaves and roots were 
found to be more infested and Navicula, Nitzschia and 
Pleurosigma form the characteristic diatoms assoc- 
iated with seagrasses”. Large numbers of fungi have 
also been reported in association with seagrass'”. Nine 
species of fungi have been recorded in association with 
Thalassia hemprichii in India'“'. Microbial flora actively 
mineralize seagrass litter and constitute about 1-3 
percent of detrital biomass'’. The epiphytes contribute 
7.5-52 percent of total seagrass ecosystem biomass in 
shallower (1-3 m] depths. The higher epiphytic biomass 
(Figure 9.1b) results mostly from algal genera such as 
Melobesia, Hypnea, Ceramium and Centroceros. The 
intensity of epiphytization increases with shoot age and 
decreases at depths of more than 3 m. 

Epifauna mostly consist of protozoans, 
nematodes, polychaetes, rotifers, tardigrades, cope- 
pods, amphipods and chironomid larvae. Very few 
attempts have been made to explore the faunal 
diversity of the seagrass beds of India. Harpacticoids, 
nauplii and nematodes are rarely found on seagrasses 
from India’. 



Most of the algal groups in marine seagrass beds 
grow on coral or shell debris, and on seagrass stems 
and roots, in their earlier stages. Later stages of these 
algae become detached and float in the waters overlying 
the meadows. Some 100 species of algae have been re- 
ported from seagrass in various regions of India {Table 
9.3). The algal flora in general is dominated by Ulva 
lactuca, Ulva fasciata, Boodlea composita, Chaeto- 
morpha linum, Halimeda spp., Chnoospora implexa, 
Chnoospora minima, Dictyota bartayresiana, Dictyota 

Table 9.1 
Quantitative data for major seagrass beds in Indian waters 

Region No. of Biomass Area 
species (g dry weight/m’) (km?) 

Southeast coast 14 2.5-21.8 30 

(Gulf of Mannar 

and Palk Bay) 


group of islands 

Nicobar group 

of islands 

West coast 

Notes: - no data available 

Source: Various sources’® *2%2") 

dichotoma, Dictyota divaricata, Hydoclathrus clathratus, 
Gracilaria edulis, Hypnea musciformes, Amphiroa 
fragillissima, Amphiroa rigida, Centroceros clavilatum 
and Centroceros spp. Coralline algae, particularly 
Halimeda spp., contribute substantially to the formation 
of sediments suitable for the growth of the seagrasses”. 
Most of the associated algal biomass contributes organic 
matter to the seagrass environment. 

Phytoplankton in the water column over the 
seagrass beds largely belong to Bacillariophyceae and 
Dinoflagellata; their occurrence is mostly patchy and 
the population density remains very low. The 
phytoplankton from the seagrass beds of Lakshadweep 
was reported to comprise 13 species (Table 9.3}, 
commonly represented by Achnanthes longipes, 
Asterionella japonica, Diploneis weisfloggi, Navicula 
hennedyii, Pinnularia sp., and Trichodesmium sp. 
Absolutely no information exists on nanoplankton and 
picoplankton from the seagrass environment of India. 

The regions of India that are colonized by sea- 
grasses support rich and diverse fauna! 7". Hard 
corals, sea anemones, mollusks, sea cucumbers, star- 
fishes and sea urchins are common invertebrates. 
Vertebrates such as fish and turtles commonly occur in 

seagrass beds; however, Dugong dugon, the marine 
mammal ({dugong), has been very rarely reported in 
recent years”. The fish fauna is reported to consist of 
192 species, dominated by sardine, mullet, eel, cat- and 
parrotfishes and grouper™'. The mollusks (143 
species}, crustaceans (150 species) and echinoderms 
(77 species] are also found in large numbers (Table 9.3). 
Mollusks are mostly represented by Acanthopleura 
spiniger, Acniaea stellaris, Conus generalis, Cypraea 
figris and Nerita costata. There are four species of sea 
turtle, with Chelonia mydas and Lepidochelys olevacea 
being common. 

The biomass and species richness of meiofauna 
and macrofauna in general is relatively very high in the 
seagrass beds compared to unvegetated areas in the 
vicinity". Sediment organic content from seagrass 
beds varies from 4 to 13 percent, ten times higher than 
the sediments from unvegetated areas. 

The textural characteristics of the sediment may 
be of great significance in determining density of 
seagrass growth. Well-established seagrass meadows 
influence mean size, sorting, skewness and shape of the 
accumulated sedimentary particles’. The sediments 
from seagrass beds of the Lakshadweep Islands show a 
significant correlation coefficient (r = 0.85, p<0.05) 
between kurtosis and total biomass, indicating 
prevalence of a relict environment'™!. This means that 
the depositional environment, which developed from 
coral reef biota over geological time, is most suitable for 
seagrass growth, a concept supported by the occurrence 
of major seagrass beds in association with coral reef 
regions *:** Halophila beccarii, an estuarine sea- 
grass, acts as pioneer species in the succession process 
leading to mangrove formation in India’”*. Thus, 
seagrasses play a very important role as basic land 
builders and shore stabilizers, in a similar way to sand 
dunes and mangroves. 


Seagrass habitats are mainly limited to mud flats and 
sandy regions from the lower intertidal zone to a depth 
of ca 10-15 m along the open shores and in the lagoons 
around islands’®. The major seagrass meadows in 
India occur along the southeast coast (Gulf of Mannar 
and Palk Bay), and a number of islands of 
Lakshadweep in the Arabian Sea and of Andaman and 
Nicobar in the Bay of Bengal. The largest area (30 km’) 
of seagrass occurs along the Gulf of Mannar and Palk 
Bay, while it is estimated that ca 1.12 km’ occur in the 
lagoons of major islands of Lakshadweep" (Table 9.1). 
A total 8.3 km* of seagrass cover has been reported 
from the Andaman and Nicobar Islands, a large portion 
of which is confined to islands like Teressa, Nancowry, 
Katchall and Great Nicobar”. Seagrasses have been 
reported to occur in long or broken stretches, or small 

Regional map: Africa, West and South Asia 


wy 0002 O09 O02! 


fo dog 

008 00r 






“fo fing 




Photo: J. Brock 

Patch reef in Florida (USA). Dark areas are seagrass meadows. Light areas around the coral heads (25-50 m diameter] are haloes created by 
herbivorous fish which live in the corals and graze on the seagrass 

Photo: FT. Short 

Photo: R. Coles, DPI 

Commercial ship aground on a seagrass flat in Australia’s Great Barrier Reef. 

Photo: F.T. Short 

Seagrass beds on the flats adjacent to an Indonesian community are 
Epiphytic algae growing on Zostera marina, Ninigret Pond, being destroyed by boat traffic, fishing activities and waste discharge, in 
Rhode Island, USA contrast to the healthy seagrasses across the channel (lower left} 

— Gulf of Kutch 

Gulf of 


Bay of 

.* Kadmatl % 
Lakshadweep Palk Bay 
(Laccadive Islands) 2 
Kalpeni | “ 
Pi s SRi 4 
0 100 200 300 400 500 Kilometers Mannar® ANA 
Cs | 
Map 9.1 

to large patches”’*". The maximum seagrass cover, 
abundance and species richness are generally found in 
the sandy regions along the seashores, and in the 
lagoons of islands, where salinity of overlying waters 
remains above 33 psu throughout the year (Table 9.2). 
The estuaries, bays, lakes and gulf regions harbor a 
limited number of seagrass species in the lower 
intertidal mud flats in regions of moderate to high (10- 
40 psu) salinity during pre-monsoon (March-June) and 
post-monsoon (November-February) periods”. During 
the monsoon itself (July-October) the seagrass beds, 
particularly estuarine seagrasses, are subject to 
freshwater flooding and become silted and decay’. 
The new growth of estuarine seagrasses starts during 
August-September with a gradual increase in salinity, 
and attains maximum growth during November- 

December, and May-June”. 


The seagrasses of India consist of 14 species belonging 
to seven genera (Table 9.2]. The Tamil Nadu ({southeast] 
coast harbors all 14 species, while eight and nine 
species have been reported from the Lakshadweep and 
Andaman-Nicobar groups of islands, respectively. The 
mainland east coast supports more species than the 
west coast of India. The main seagrasses are Thalassia 
hemprichii, _Cymodocea_ rotundata, Cymodocea 
serrulata, Halodule uninervis and Halophila ovata. 
Species such as  Syringodium  isoetifolium 
and Halophila spp. occur in patches as mixed 
species. Meadows are mostly heterospecific. However, 




Andaman # 

} Islands 


Little Andaman 


Ten Degree Channel 

« Car Nicobar 

leressa * 

a) a 
\ ; Camora 
eS Nancowry 



Little Nicobar 

Great Nicobar 

0 20 40 60 80 100 Kilometers 
EL las 

Map 9.2 
Andaman and Nicobar Islands 

from Kalpeni and Kadmat Islands of Lakshadweep, 
plant composition is bispecific and monospecific, 
respectively'”. Gulf and bay estuaries mostly harbor low 
numbers of species, dominated by Halophila beccarii in 
the lower intertidal regions, and by Halophila ovalis in 
the lowest littoral zones. Enhalus acoroides has 
restricted distribution in the mid-intertidal swampy 
regions and shallow brackish waters” ''”. 

Seagrasses grow from the regularly inundated 
intertidal zone to ca 15 m depth in the sandy subtidal 
zones". Unlike other species, Halophila beccarii is 
found in the upper intertidal. The maximum number 
of species and highest biomass usually occur at the 





depth of 1-2.5 m (Figure 9.1]. The biomass of major 
seagrass beds has been reported to be significantly 
(r = -0.63 and -0.71, p<0.05) correlated with depth” '”. 
Thalassia hemprichii, Cymodocea_ rotundata, 
Cymodocea serrulata and Halophila ovata are 
well adapted to the poor ambient light at greater 
depths [>3 m]. 

Biomass of Indian seagrasses varies from 180 to 
720 g wet weight/m’* [see also Table 9.1]. Halodule 
uninervis and Cymodocea rotundata in the shallower 
depths (0.5-2.5 m), and Thalassia hemprichii and 
Cymodocea serrulata from the deeper [>3 m) waters, 
are the main contributors to biomass along the 
southeast coast (Figure 9.1]. A similar trend of 
distribution and abundance was observed from major 
seagrass beds of Lakshadweep Islands in the Arabian 
Sea". The lower biomass and reduced number of taxa in 
seagrasses deeper than 2 m is mainly attributed to 
insufficient ambient light. The older plants provide sub- 
stratum for colonization by epiphytes, which make a 

Table 9.2 
Occurrence of seagrasses in coastal states of India 

Seagrass sp. 

Cymodocea rotundata 
Cymodocea serrulata 
Enhalus acoroides 
Halodule pinifolia 
Halodule uninervis 
Halodule wrightii 
Halophila beccarii 
Halophila decipiens 
Halophila ovalis 
Halophila ovalis var. ramamurtiana 
Halophila ovata 
Halophila stipulaceae 
Syringodium isoetifolium 
Thalassia hemprichii 
Ruppia maritima 

Total no. of species 

Status of seagrass ecosystem 
Salinity (psu) 


considerable contribution to total seagrass system 
biomass” '”. Biomass of Halophila beccarii is reported 
to vary from 4 to 24 g wet weight/m* with a minimum in 

the month of August and a maximum in October™. 


The natural causes of seagrass destruction in India are 
cyclones, waves, intensive grazing and infestation of 
fungi and epiphytes, as well as “die-back” disease. 
Exposure at ebb tide may result in the desiccation of 
the bed. Strong waves and rapid currents generally 
destabilize the meadows causing fragmentation and 
loss of seagrass rhizome. The decrease in salinity due 
to excessive freshwater runoff also causes dis- 
appearance, particularly of estuarine seagrass beds in 
the confluence regions. 

Anthropogenic activities such as deforestation in 
the hinterland or mangrove destruction, construction of 
harbors or jetties, and loading and unloading of 
construction material as well as anchoring and moving 


States: GJ Gujarat; MH Maharashtra; G Goa; KA Karnataka; KL Kerala; LD Lakshadweep Islands; WB West Bengal; OR Orissa; AP Andhra Pradesh; 

TN Tamil Nadu; A&N Andaman and Nicobar Islands. 

Frequency of occurrence: - absent; + very rare; ++ rare; +++ common; ++++ dominant. 
Status of seagrass ecosystem: VG very good; G good; D degraded; MD most degraded; C in the process of formation. 

Source: Various sources ® % 12. 20.291. 

Table 9.3 
Associated biota of seagrass beds of India 

Group Number of species 

Bait fishes 21 
Ornamental fishes 138 
Fin fishes 







Marine algae 



Source: Various sources!” ® 720-22) 

of boats and ships, dredging and discharge of sediments, 
land filling and untreated sewage disposal, are some of 
the major causes of seagrass destruction in India. As a 
result of the above natural and anthropogenic activities, 
the sediment load in the overlying waters of seagrass 
beds increases, reducing the amount of ambient light, 
resulting in lower productivity because of a decline in 
photosynthetic processes and increased respiration. The 
excess sediment input in the region results in the 
siltation and decline of seagrass beds. The siltation of 
seagrass beds has been commonly observed in the Gulf 
of Kutch, Gujarat, Andaman and Nicobar Islands, and in 
most of the estuaries. 

Seagrass beds in the lower intertidal region in the 
Gulf of Kutch and a number of islands have experienced 
decline. Halophila decipiens, reported earlier” along 
the west coast, has totally disappeared, which might be 
due to its elimination during natural succession. 
Overexploitation of fisheries, particularly sea cucum- 
bers and sea urchins, has impacted the resources 
associated with seagrass beds. Dugong dugon, which 
was abundant five decades ago’, has totally dis- 
appeared along the Indian coast. The last report of 
dugong sightings dates back to 1994-95 in Andaman 
waters”. The loss of this mammal from the Indian 
coast could be attributed to overexploitation for fat and 
meat, as well as the obvious declines in seagrass beds. 


In India, seagrass regions, along with mangroves and 
corals, have been categorized as ecologically sensitive 
ecosystems under the Coastal Regulation Zone 
Notification to the Environment (Protection) Act’. 

However, seagrasses in India have been largely left out 
of education, research and management compared to 
other ecologically sensitive habitats such as mangroves, 
sand dunes and corals. Considering the lack of 
awareness, limited distribution and rising anthropo- 
genic pressures, it is imperative to develop a national 
educational and conservation management plan for the 
seagrass ecosystem with the following objectives: 

) quantification, mapping and regular monitoring to 

evaluate changes over time; 

) education, research and awareness programs; 

fo) environmental impact assessments; 

) mitigation of adverse impacts; 

) identification and conservation of areas as 
germplasm centers; 

) rehabilitation. 

Figure 9.1 

Abundance of seagrass species at various depths in the Gulf of 
Mannar (southeast coast) 

\ Halodule 







Depth (m) 

5 Total 
ls Epiphytic 
Ml Seagrass 

Average biomass (g dry weight/m?] 

Figure 9.1b 



Case Study 9.1 

Kadmat Island is located at 11°10°52"-11°15°20"N 
and 72°45'41"-72°47 29'E. It stretches ca 8 km from 
north to south, ranging in width from ca 50 to ca 400 
m, with an area of 3.12 km*. The lagoon is on the 
leeward [western] side, with a depth of 2-3 m. The 
storm beach along the eastern side has an average 
width of ca 100 m. A coralline algal ridge occurs 
along the breaking zone of the storm beach. The 
island is a submarine platform with a coral reef in 
the form of an atoll. It is crescent-shaped, having a 
north-south orientation. The western margin of the 
lagoon is a submarine bank marked by a narrow 
reef below. 

Sampling and observations occurred along five 

fixed transects laid down from -10 m on the reef 
slope up to ca 150-200 m above high-tide line on the 
island. The length of the transect varied from ca 1 to 
3.5 km depending upon the topography or the 
contour. The samplings were done during the post- 
monsoon [November 1998] and pre-monsoon (May 
1999] seasons. The collections and observations 
were made from depths of -10 m and -5 m on the 
reef slope and from -1.5 and -2.5 m in the lagoon, 
and from exposed flats of reef and storm beach . 
The seagrass bed in Kadmat Lagoon occurs In 
patches as well as longer stretches along the shore. 
A dense meadow occurs towards the northwest 
region of the lagoon covering some 0.14 km? and 

Characterization of a seagrass meadow at Kadmat Island, Lakshadweep 

Period November 1998 
Zone Lagoon Mid-lagoon 
towards region 
fore reef 
Depth (m) 1-1.5 1.5-2.5 
Substratum S+CD S 
Thickness of substratum (cm) >2.5 5-10 
Sand % (range) 97.1-97.95 97.8-98 
Silt % {range} 0.23-2.8 1.67-1.82 
Clay % (range) 0.1-2.03 0.32-0.42 
Organic carbon (%) 0.11-0.27 0.21-0.23 
Nature of seagrass beds SP LP 

Quantitative aspect of seagrasses 

Number of seagrass species 1 2 
Thalassia hemprichii 
% frequency of occurrence 10-20 10-20 
Biomass (g dry weight/m’) N 5 
Cymodocea rotundata 
% frequency of occurrence A 10-20 
Biomass (g dry weight/m’) NA 15 
Total biomass (g dry weight/m’) NA 20 
Average total drifted biomass NA NA 
(g dry weight/m?) 

- data not collected 

March 1999 
Lagoon Lagoon Mid-lagoon Lagoon 
towards towards region towards 
land fore reef land 
0-0.5 1-1.5 1.5-2.5 0-0.5 
>10 >2.5 5-10 >10 
94.8-97.6 - - - 
2.02-2.48 - - - 
0.41-2.74 - - - 
0.36-0.42 1.08-1.4 1.52-1.96 0.92-1 
1 2 2 1 
A 10-20 50-70 A 
NA N 75 NA 
50-70 - 50-70 >70 
17 - 23 26 
17 N 30.5 26 
N NA NA 195 

S sandy; CD coral debris; SP small patches; LP large patches; BS broken stretches 

A absent; N negligible; NA not applicable 

Source: Desai et al.'°*! 

exhibiting marked zonation. Mostly sparse and small 
patches of Thalassia hemprichii occur in the shallow 
sandy regions towards the fore reef, while the mid- 
lagoon deeper region [1.5-2.5 m] harbors mixed 
dense beds of Thalassia hemprichii and Cymodocea 
rotundata. The shallow region (0.5-1.5 m) towards 
land supports intensive growth of Cymodocea 
rotundata. A similar kind of distribution trend has 
been reported from the other islands on the 
Laccadive Archipelago”. The seagrass flora of 
Kadmat comprises two species with higher biomass 
(20-35 g dry weight/m*) occurring from the mixed 
zone in the mid-lagoon (see table, left]. A biomass of 
drifting seagrasses {195 g dry weight/m*] was 
recorded during March when the biomass of the 
seagrass standing crop was higher (26 g dry 
weight/m’]. The frequency of occurrence of drifting 
seagrass increased from 20 percent to 70 percent 
during March, reflecting seagrass maximum bio- 
mass; it is during this pre-monsoon period that high 
wind speeds cause disturbances in the state of the 
sea, including lagoon waters. Previously, five species 
of seagrasses were recorded from the lagoons of 
Kadmat”". It has been observed that the small-sized 
seagrasses, such as Halophila spp., commonly grow 
as pioneer species and form a suitable substratum 
for other larger-sized seagrasses to follow during the 
succession process". The absence of such species 
from Kadmat Lagoon during this study might be due 
to competition by the existing species during 

A considerable amount of seagrass biomass 
contributes to the detrital food chain’. The benthic 
faunal population from the seagrass beds has been 
reported to be higher due to high organic carbon in 
the sediments". The organic carbon in the sedi- 
ments, particularly from the seagrass beds, varied 
from 0.11 to 1.96 percent (see table, left]. Macro- 
fauna from the seagrass bed of Kadmat Island 
consisted of eight groups [see table, right). 
Macrofauna were largely Oligochaeta (40.17 
percent), but the maximum number of species (22) 
were from Polychaeta group™’. It was reported 
earlier that Polychaeta [44.6 percent] and Crustacea 
(42 percent] constitute the major macro- 
invertebrates in the seagrass beds of India'™”. 

The composition of meiofauna in seagrasses 
varies seasonally"”. The meiofauna from the 
seagrass bed of Kadmat'™” is represented by 19 
groups dominated by Turbellaria (34.2 percent), 
Nematoda (37.3 percent] and herpacticoid copepods 
(10.1 percent). 

Thalassia hemprichii 

Benthic macrofauna in the seagrass bed at Kadmat Island, 

Macrofauna No.of No. of % Dominant 

group genera species composition taxa 

Polychaeta 20 22 18.96 | Lumbriconeries, 
Syllis, Onuphis, 

Nematoda 1 1 18:71 = 

Oligochaeta 1 1 40.17 - 

Pelecypoda 3 3 2.96 |Mesodesma, 

Gastropoda 8 8 2.32 Cerithium, 

Crustacea 6 6 11.36 | Amphipoda, 

Ophiuroidea i 1 0.61 Echiurida 

Ascheliminthes - - 447 - 

Unidentified = = 0.44 - 

Note: - not identified to genus/species level 

Source: Branganza et al.'*” 





The Ministry of Environment and Forests, 
Government of India, coordinates environment and 
biodiversity-related coastal zone management 
programs in the country. This department has a vital 
role in adapting and implementing educational and 
management plans for the seagrass environments of 
India, similar to those for mangrove and coral reef 
habitats. The necessary inputs based on research 
would be of great importance in the formation of a 
national seagrass management plan. Hence, the 
ministry must encourage universities and national 


1 Anon [1992]. ‘Coastal Environment’ A Remote Sensing Application 
Mission. A Scientific Note by Space Application Center (ISRO), 
Ahmedabad, funded by Ministry of Environment and Forests, 
Government of India, SAM/SAC/COM/SN/11/92. 100 pp. 

2 Santapu H, Henry AN [1973]. A Dictionary of the Flowering Plants 
in India. CSIR Publication, New Delhi. 

3 Untawale AG, Jagtap TG [1978]. A new record of Halophila beccarii 
(Aschers] from Mandovi estuary, Goa, India. Mahasagar, Bulletin of 
the National Institute of Oceanography 10: 91-94. 

4 Lakshmanan KK [1985]. Ecological importances of seagrass in 
marine plants, their biology, chemistry and utilization. In: 
Krishnamurthy V (ed) All India Symposium Marine Plants, 
Proceedings. Donapaula, Goa. pp 277-294. 

5 Ramamurthy K, Balakrishnan NP, Ravikumar K, Ganesan R [1992]. 
Seagrasses of Coromandel Coast, India. Flora of India, ser. 4. BSI, 
Coimbatore. 79 pp. 

6 Jagtap TG, Untawale AG [1981]. Ecology of seagrass bed Halophila 
beccarii (Aschers} in Mandovi estuary, Goa. /ndian Journal of 
Marine Sciences 4: 215-217. 

7 Jagtap TG [1987]. Distribution of algae, seagrass and coral 
communities from Lakshadweep Islands, Eastern Arabian Sea. 
Indian Journal of Marine Sciences 16: 56-260. 

8 Jagtap TG [1991]. Distribution of seagrasses along the Indian 
Coast. Aquatic Botany 40: 379-386. 

9 Jagtap TG [1996]. Some quantitative aspects of structural 
components of seagrass meadows from the southeast coast of 
India. Botanica Marina 39: 39-45. 

10 Jagtap TG [1998]. Structure of major seagrass beds from three 
coral reef atolls of Lakshadweep, Arabian Sea, India. Aquatic 
Botany 60: 397-408. 

11 Untawale AG, Jagtap TG [1989]. Marine macrophytes of Minicoy 
(Lakshadweep) coral atoll of the Arabian Sea. Aquatic Botany 19: 

12 Ansari ZA [1984]. Benthic macrofauna of seagrass (Thalassia 
hemprichii) bed at Minicoy, Lakshadweep. Indian Journal of Marine 
Sciences 13: 126-127. 

13. Ansari ZA, Rivonker CV, Ramani P, Parulekar AH [1991]. Seagrass 
habitat complexity and microinvertebrate abundance in 
Lakshadweep coral reef lagoons, Arabian Sea. Coral Reefs 10: 127- 

14 Sathe V, Raghukumar S [1991]. Fungi and their biomass in detritus 

of the seagrass Thalassia hemprichii (Ehrenberg) Ascherson. 

Botanica Marina 34: 271-277. 

Jacobs RPWM [1982]. A Report: Component Studies in Seagrass 

Ecosystems along West European Coasts. DRUK: Drukkerij verweij 

BV, Mijdercht. pp 11-215. 

Bortone SA [1999]. Seagrasses: Monitoring, Ecology, Physiology 

and Management. CRC Press, New York. 309 pp. 

Larkum AWD, McComb AJ, Shepherd SA [1989]. Biology of 

Seagrasses. Elsevier, New York. 841 pp. 




laboratories to undertake investigations on the various 
aspects of seagrass ecosystems. 

The authors are grateful to the Director of the National Institute of 
Oceanography (CSIR), Donapaula, Goa, for his encouragement. 


T.G. Jagtap, D.S. Komarpant and R. Rodrigues, National Institute of 
Oceanography, Dona Paula, Goa - 403004, India. Tel: +91 (0)832 456700 
4390. Fax: +91 (0}832 456702/456703. E-mail: tanaji( 

18 Cuomo V, Jones EB, Grasso S [1988]. Occurrence and distribution 
of marine fungi along the coast of the Mediterranean Sea. Progress 
in Oceanography 21:189-200. 

19 Siddique HN [1980]. The ages of the storm beaches of the 
Lakshadweep (Laccadive]. Marine Geology 38: M11-M20. 

20 Das HS [1996]. Status of Seagrass Habitats of Andaman and 
Nicobar Coast. SACON Technical Report No. 4, Coimbatore. 32 pp. 

21 Jagtap TG, Inamdar SN [1991]. Mapping of seagrass meadows from 
the Lakshadweep Islands [India], using aerial photographs. J Ind 
Soc Remote Sensing 19: 77-81. 

22 James PSBR [1989]. Marine living resources of the union territory 
of Lakshadweep - an indicative survey with suggestions for 
development, Cochin, India. CMFRI Bulletin 43: 256 pp. 

23 Swinchatt JP [1965]. Significance of constituent composition, 
texture and skeletal breakdown in some recent carbonate 
sediments. Journal of Sedimentary Petrology 35: 71-90. 

24 Rajamanickam GV, Gujar AR [1984]. Sediment depositional 

environment in some bays in the central west coast of India. Indian 

Journal of Marine Sciences 53-59. 

Hackett HE [1977]. Marine algae known from Maldive Islands. Atoll 

Research Bulletin 210: 2-37. 

26 Fortes MD [1989]. Seagrass: A Resource Unknown in the Asian 

Region. ICLARM, Manila. 46 pp. 

Jagtap TG [1985]. Ecological Studies in Relation to the Mangrove 

Environment along the Goa Coast, India. PhD thesis, Shivaji 

University, Kolhapur. 212 pp. 

28 Untawale AG, Jagtap TG [1991]. Floristic composition of the deltaic 
regions of India. In: Vaidyanadhan R led) Quaternary Deltas of India, 
Memoir 22. Publication GSI, Bangalore. pp 243-265. 

29 Jagtap TG [1992]. Marine flora of Nicobar group of Islands, 
Andaman Sea. Indian Journal of Marine Sciences 22: 56-58. 

30 Parthasarthy N, Ravikumar K, Ramamurthy K [1988]. Halophila 
decipens Ostenf. Southern India. Aquatic Botany 32: 179-185. 

31. Nair RV, Lal Mohan RS, Roa KS [1975]. The Dugong {Dugong 
dugon). CMFRI Bulletin. 42 pp. 

32 Anon [1990]. Coastal area classification and development 
regulations. Gazette Notification, Part II, Section 3 [ii], Govt of India, 
No. SC 595 (F] - Desk - 1/97. 

33 Birch WR, Birch M [1984]. Succession and pattern of tropical 
intertidal seagrasses in Cockle Bay, Queensland, Australia: A 
decade of observation. Aquatic Botany 19: 343-368. 

34 Mann KH [1988]. Production and use of detritus in various fresh 
water, estuarine and marine ecosystems. Limnology and 
Oceanography 33: 910-930. 

35 Branganza C, Ingole BS, Jagtap TG. Unpublished data. 

36 Desai W, Komarpant DS, Jagtap TG [Accepted manuscript]. 
Distribution and diversity of marine flora in coral reef ecosystems 
of Kadmat Island in Lakshadweep Archipelago, Arabian Sea, India. 
Atoll Research Bulletin. 





10 The seagrasses of 

Western Australia 


km, from the temperate waters of the Southern 

Ocean at 35°S to the tropical waters of the Timor 
Sea at 12°S, with the contiguous coastline of the 
Northern Territory extending across to Queensland. 

T« coastline of Western Australia extends 12500 


The long coastline has a diversity of environments that 
support seagrass, ranging from those tropical species 
associated with coral reefs and mangroves in the north 
to large temperate seagrasses, in the shelter of 
limestone reefs and in large embayments, on the west 
and south coasts. These are exposed to different tidal 
conditions {amplitudes 9 m in the north to less than 1m 
on the west and south coasts"), substratum types and 
exposure to wave energy. Although some areas of the 
Western Australian coast, such as Cockburn Sound, 
have been the subject of much research, a great deal of 
the rest of the marine environment is poorly described 
or understood. 

This chapter will provide a brief description of the 
coastal geomorphology, seagrass species and habitats, 
and their biogeography. Current uses will be described 
and current and potential threats to these habitats/ 
uses considered. Extensive use of Environment 
Western Australia 1998: State of the Environment 
Report” and of The State of the Marine Environment 
Report®“ has been made in compiling the latter section 
of this review. Issues of seagrass management will also 
be discussed. 

Geomorphology of the coast 

The underlying geology of the coast consists of granitic 
rocks in the south and southwest, with extensive 
mantling of tertiary limestone, and sandstones in the 
northwest and north. In the southeast of the state, the 
vertical limestone cliffs of the southern edge of the 
Nullarbor Plain delimit a narrow coastal plain. For 

D.1. Walker 

almost 300 km, offshore reefs protect sandy beaches 
and high foreshore sand dunes from oceanic swell, 
producing a calmer habitat between the reefs and the 
shore, suitable for seagrass growth. At Twilight Cove 
the cliffs again approach the sea and follow the 
coastline to just east of Israelite Bay. From there to 
Esperance, beaches and seagrass beds are sheltered 
by the granitic islands of the Recherche Archipelago, 5- 
50 km offshore. 

From Esperance to Albany, sheltered beaches are 
broken by granite outcrops although occasionally 
limestone reefs and eroded cliffs occur. Small rivers 
flow into a number of bays along this 500-km coastline, 
but they have relatively low discharge rates, 
particularly during the summer dry season. Offshore of 
these estuaries, seagrasses of the Posidonia 
ostenfeldii group occur as they can withstand swell and 
sediment movement. 

From Albany to Cape Naturaliste, limestone 
overlies granitic rocks for much of the coast. 
Seagrasses occur in this region in sheltered inshore 
lagoons protected by offshore reefs. 

Geographe Bay, east of Cape Naturaliste, is north 
facing and the prevailing southwesterly swell is 
refracted into the relatively sheltered embayment. The 
embayment has a thin sediment veneer (mean 
thickness: 1 m] overlying Pleistocene limestone”. It 
provides an ideal habitat for seagrasses, and 
extensive meadows are found to depths of 25 m. 
A number of estuaries, larger than those further east, 
also afford habitat for seagrasses and other submerged 
aquatic plants such as Ruppia”" and their associated 

The western coastline, from Geographe Bay to 
Kalbarri, is relatively straight and continuous, as it has 
been eroded by the action of winds and currents which 
have built up sand dunes and bars parallel to the coast. 
There is also a fringe of limestone reefs running 



parallel to the coast which are relict Pleistocene dune 
systems composed of aeolianite; these break the Indian 
Ocean swells, forming relatively calm, shallow (4-10 m 
deep) lagoons up to 10 km wide, in which the tidal 
range is small {<1 m), and the waters generally clear. 
These lagoons are dominated by seagrasses. 

From Kalbarri to Steep Point (the most westerly 
point of the mainland], along Dirk Hartog Island, 
Bernier and Dorre Islands and up to Quobba Point, 
there are high cliffs composed of sandstone to the 
south and limestone to the north. These cliffs shelter 
Shark Bay, a large (13000 km’), shallow, semi- 
enclosed embayment (see Case Study 10.1). This is an 
area of intense carbonate sedimentation, which is 
affected by wind and tidal-driven water movement, 
leading to high turbidity. It also has relatively low water 
temperatures in winter (down to 13°C)". 

North of Quobba Point, the Pilbara coastline has a 
low relief with gently sloping beaches, numerous 
headlands and many small offshore islands. Headlands 
are composed of isolated patches of very hard 
hematite-bearing quartzite, which is more resistant to 
erosion than the surrounding rocks. Normal erosion 
processes, combined with submergence, have led to a 
broken, rough coastline. Mangroves become conspic- 
uous. Coral reefs and atolls occur north of Quobba 
Point (near the Tropic of Capricorn), where tropical 
seagrasses are found in lagoons, as well as in 
mangrove swamps and around islands’. There is a 
progressive increase in tidal amplitude with decreasing 
latitude. Large tides affect seagrass distributions by 
resuspending sediments; the high turbidity limits 

Table 10.1 
Western Australian endemic seagrass species 

Species Distribution 

Amphibolis antarctica 
Amphibolis griffithii 
Cymodocea angustata 

Southern Australian endemic 
Southern Australian endemic 
Tropical Western Australian 
Thalassodendron pachyrhizum Southern Australian endemic 
Halophila australis 
Posidonia angustifolia 
Posidonia australis 

Australian endemic 

Southern Australian endemic 
Southern Australian endemic 
Western Australian endemic 
Southern Australian endemic 
Western Australian endemic 
Western Australian endemic 
Southern Australian endemic 

Posidonia coriacea 
Posidonia denhartogii 
Posidonia kirkmanii 
Posidonia ostenfeldii 
Posidonia sinuosa 

seagrass growth to shallow water. On broad intertidal 
flats, seagrasses are restricted to those species which 
can tolerate high temperatures and desiccation, as well 
as periodic freshwater inundation from rainfall. 

The Kimberley coast is a typical ria (drowned river 
valley) system, characterized by resistant basement 
rock, with faults oriented at angles to the shore, 
creating a rugged coastline. The area is subject to large 
tidal amplitudes and is remote and sparsely populated, 
with little information available about the marine 
habitats. Embayments and sounds grade shorewards 
into mangrove-covered tidal flats, and there are many 
offshore islands. Extensive terracing of these expanses 
of the intertidal zone often results in seagrass, 
particularly Enhalus acoroides", high in the intertidal 
just below the mangroves. 

Much of the Kimberley landscape is of 
extraordinary natural beauty, extending to its coastal 
regions. With a vast land area and a small population, 
the Kimberley has been, until recently, largely 
unexplored by biologists. Its isolated coastline is 
devoid of settlement along the 2000-km stretch 
between Derby and Wyndham. The area is receiving 
growing attention from tourists, with increasing 
activity by small private boats and charter operators. 
As part of the development of a marine park and 
reserve system in Western Australia, several areas are 
being considered as potential marine parks. In 
addition, some of the areas have been designated as 
potential Aboriginal reserves. These designations have 
been based on severely limited data available from the 
few scientists and other people who have traveled in 
the area. The only substantial data on marine 
organisms in the Kimberley relate to salt water 
crocodile populations and turtles. Marine plants, fish 
and invertebrates are largely unknown. Recent surveys 
by the West Australian Museum, the University of 
Western Australia and the Northern Territory Museum, 
and by CSIRO [Australia’s Commonwealth Scientific 
and Industrial Research Organisation], have yet to be 
published, but will help provide a basis for future 


Seagrasses recorded from Western Australia fall into 
two general distribution patterns. Twelve species are 
endemic to Western Australia or to the southern 
Australian coast, and are confined to temperate, clear 
waters [Table 10.1). Twelve species are tropical and 
are found throughout the Indian Ocean and tropical 
Pacific Ocean. 

Australia’s seagrasses can be divided into 
temperate and tropical distributions, with Shark Bay on 
the west coast and Moreton Bay on the east coast being 
located at the center of the overlap zones. Temperate 

species have been studied most extensively, 
particularly the large genera Amphibolis, Posidonia 
and Zostera, but there are other species which have 
been little studied. Temperate species are distributed 
across the southern half of the continent, extending 
northwards on both the east and west coasts. The 
highest biomasses, and highest regional species 
diversity, occur in southwestern Australia, where 
seagrasses are found in the coastal back-reef 
environments within the fringing limestone reef, or in 
semi-enclosed embayments. 

In areas of northern Australia with a high tidal 
range, visibility is often poor, and conventional remote- 
sensing techniques are of limited value for mapping. 
The Northern Territory coastline is largely unexplored 
for seagrass distribution, and their associated animal 
communities, especially the Northern Territory prawn 
fisheries, remain largely unstudied. Recent research in 
the Kimberley region of Western Australia has provided 
some distribution information. Seagrasses in that 
region either occur sparsely in coral reef environments 
or can attain high biomasses within high intertidal 
lagoons, where seawater is ponded during the falling 
tide". The environments are otherwise too extreme 
(tidal movements/turbidity/freshwater runoff in the wet 
season] for seagrass survival”. Again, the significance 
of these seagrass communities for any associated 
fisheries species is unknown. 

In general, our knowledge of shallow water 
(<10 m) temperate seagrass distributions is reasonably 
good, but our understanding of deep water [>20 m) 
seagrasses throughout Australia is rudimentary. Areas 
subject to more extreme water movement, either tidal 
or wave induced, are also poorly studied compared with 
seagrasses in more protected areas. 

The main habitats for seagrasses are very 
extensive shallow sedimentary environments that are 
sheltered from oceanic swell, such as embayments 
(e.g. Shark Bay, Cockburn Sound), protected bays (e.g. 
Geographe Bay, Frenchman’s Bay] and lagoons 
enclosed by fringing reefs {e.g. Bunbury to Kalbarri). 
Seagrasses occupy approximately 20000 km* on the 
Western Australian coast', ranging in depth from the 
intertidal to 45 m'“!, making up a major component of 
nearshore ecosystems. The diversity of seagrass 
genera (10) and species (25) along this coastline is 
unequaled elsewhere in the world'”, mainly due to the 
overlap between tropical and temperate biogeographic 
zones, and the extent of suitable habitats. 

Large, mainly monospecific meadows of 
southern Australian endemic species form about one 
third of the habitat in the coastal regions of Western 
Australia. These meadows have high biomasses 
(500-1000 g/m*) and high productivities (>1000 
g/m*/year)'"!. Southern Australian seagrasses occur in 

Western Australia 

400 600 Kilometers 

Rowley « 

Montebello Is. 

Barrow | 

Park/ 4a 

Ee Quobba Pt. 

y Shark Bay Western Australia 

~ Steep Pt. 



Jurien Bay 

Cockburn Sound. \, a 
Geographe Bay. ( 

Cape Naturaliste va Ey 

Esperance Twilight Cove 

vn- Israelite Bay 


Cape Leeuwin Recherche 

atts aN Archipelago 

Frenchman's Bay Princess Royal Harbour 

Albany Harbour and Oyster Harbour 
120° E * 

140° E 
Map 10.1 
Western Australia 

water bodies exposed to relatively high rates of water 
movement. Nevertheless, Australian species also 
occur where there is some protection from extreme 
water movement and most are found in habitats with 
extensive shallow sedimentary environments, shel- 
tered from the swell of the open ocean, such as 
embayments [e.g. Shark Bay and Cockburn Sound}, 
protected bays (e.g. Geographe Bay and Frenchman's 
Bay) and lagoons sheltered by fringing reefs (e.g. the 
western coast from 33° to 25°S). 


Seagrass declines have been well documented from 
around Australia. There are a variety of mechanisms of 
seagrass loss, but the most ubiquitous and pervasive 
cause of decline is the reduction of light availability. 
Seagrasses are rather unique plants in that they have 
high minimum light requirements for survival 
compared with other plants'. These high minimum 
light requirements (10-30 percent incident light) are 
hypothesized to be related to the significant portions of 
seagrass biomass that can be in anoxic sediments. 
Reduction in light availability can occur as a result of 
three major factors: chronic increases in dissolved 
nutrient availability leading to proliferation of light- 
absorbing algae, either phytoplankton, macroalgae or 
algal epiphytes on seagrass leaves and stems; chronic 



D. Walker 



Intertidal Enhalus acoroides, Leonie Island, Kimberley, Western 

increases in suspended sediments leading to increased 
turbidity; and pulsed increases in suspended 
sediments and/or phytoplankton that cause a dramatic 
reduction of light penetration for a limited time period. 

Loss of habitat 

Seagrasses are limited to the photic zone, extending up 
to 54 m'”. Reductions in water quality can lead to a 
reduction in the depth of the photic zone’, and hence 
to a direct loss of habitat. Seagrasses in Cockburn 
Sound, for example, are limited to a depth of less than 
9 m, whereas in unpolluted areas the depth limit would 
be 11-15 m. Increasing population pressure in Western 
Australia leads to increasing pressure on the coast. 
Development of the coastal zone, all along the Western 
Australian coastline, in the form of construction of 
marinas, port facilities and canal estates, results in 
degradation of coastline causing direct destruction of 
seagrass communities as well as indirect changes in 
hydrodynamics and sedimentation. 

Habitat removal 

Coastal development in Western Australia is localized 
to centers of population, and takes the form of 
construction of ports, marinas and groynes. Housing 
developments impact on coastal water quality, whereas 
canal estates, such as in Carnarvon, have greater direct 
impact on the marine environment. All these develop- 
ments have potential consequences for seagrass 
habitats and associated fauna. 

Some developments have resulted in direct 
destruction of seagrass communities, by smothering or 
deterioration in water quality, e.g. construction of the 
causeway at the southern end of Cockburn Sound", 
where construction destroyed existing reef environ- 
ments, and resulted in loss of seagrass habitat due to 
reduced flushing. The construction of ports and 
marinas in the Perth Metropolitan area has degraded 
existing seagrass and reef habitats, as well as 
fragmenting the remaining distributions. Subsequent 
dredging and sediment infill has often reduced the 
water quality and resulted in further losses. 

Impacts of pollution 

Pollution of coastal environments can result in major 
changes to water quality, either from point or diffuse 
sources which can influence marine community 
structure, especially in relation to seagrass. Marine 
disposal of sewage from the Perth Metropolitan 
region's three outfalls contributes excess nutrients to 
coastal areas”. The Kwinana Industrial Strip along the 
shores of Cockburn Sound still relies on marine 
disposal of the industries’ effluents, although now 
under license conditions to regulate the amounts of 

Water quality, especially nutrients 
The Western Australian coastal environment is 
particularly sensitive to nutrient enrichment from 
human activities. The effects of this anthropogenic 
eutrophication include an increase in frequency, 
duration and extent of phytoplankton and macroalgal 
blooms", low oxygen concentrations in the water 
column, shifts in species composition’*", loss of 
seagrass and benthic vegetation’, decrease in 
diversity of organisms present’ and an increase in 
diseases in fish and waterfowl. Western Australian 
marine waters are generally low in nutrients and 
biological productivity. Serious seagrass losses 
resulting from increased nutrient loading have 
occurred in the Albany Harbours, Cockburn Sound and 
parts of Geographe Bay. Cockburn Sound is the most 
degraded marine environment in Western Australia, 
having experienced the second largest loss of seagrass 
in Australia (more than two thirds]. 

The major human-induced declines of seagrass 

in Western Australia are summarized in Table 10.2, with 
suggested principal causes - in most cases, other 
factors interact to make the process of loss more 
complex. The general hypothesis for all these instances 
of seagrass decline is that a decrease in the light 
reaching seagrass chloroplasts reduces effective 
seagrass photosynthesis. The decrease may result 
from increased turbidity from particulates in the water, 
or from the deposition of silt or the growth of epiphytes 
on leaf surfaces or stems’. Seagrass meadows occur 
between an upper limit imposed by exposure to 
desiccation or wave energy, and a lower limit imposed 
by penetration of light at an intensity sufficient for net 
photosynthesis. A small reduction in light penetration 
through the water will therefore reduce the depth range 
of seagrass meadows, while particulates on leaves 
could eliminate meadows over extensive areas of 
shallower water [e.g. Princess Royal Harbour, Western 

Increasing turbidity of water above seagrasses 
may occur directly, by discharge or resuspension of fine 
material in the water column from, for example, sludge 
dumping. Indirect effects on attenuation coefficients 
occur through increased nutrient concentrations 
resulting from the discharge of sewage and industrial 
wastes, or from agricultural activity in catchments, 
which in turn increase phytoplankton biomass reducing 
light penetration significantly’. The extent of phyto- 
plankton blooms associated with nutrient enrichment 
will be determined by water movement, and mixing will 
dilute nutrient concentrations. Deeper seagrass beds 
further from the sources of contamination may show no 
influence of turbidity. 


In Cockburn Sound, nutrient enrichment has led not 
only to enhanced phytoplankton growth but also to 
enhanced growth of macroscopic and microscopic 
algae on leaf surfaces”. Macroalgae dominate over 
seagrasses under conditions of marked eutrophication, 
both as epiphytes and as loose-lying species (e.g. the 

Table 10.2 

Western Australia 

genera Ulva, Enteromorpha, Ectocarpus) which may 
originate as attached epiphytes””. Increased epiphytic 
growth results in shading of seagrass leaves by up to 65 
percent”, reduced photosynthesis and hence leaf 
densities”. In addition, the epiphytes reduce diffusion 
of gases and nutrients to seagrass leaves. 

Light penetration 

As photosynthetically active radiation passes through 
water, it is attenuated by both absorption and 
scattering. Attenuation is increased by the presence of 
suspended organic matter (e.g. phytoplankton) and 
inorganic matter, particularly in eutrophic systems 
when phytoplankton concentrations are high'”, thus 
reducing light penetrating to benthic primary 
producers. In Cockburn Sound, where this continued 
for extended periods of time, reduction in density and 
loss of benthic macrophytes resulted!’”, 

The requirement of light by benthic macrophytes 
makes the presence of submerged aquatic vegetation 
an indicator of water quality {adequate light penetra- 
tion} and hence, nutrient status [i.e. low nutrient 
concentrations)'"”. Light reduction for extended 
periods, which is common in eutrophic systems, causes 

loss of benthic macrophyte biomass”. 


Changes in landuse practices often result in increased 
sediments in runoff from land, e.g. in Oyster Harbour. 
Larger sediment loads reduce light penetration, as 
detailed above. Increased sedimentation can result in 
changes in the abundance and percentage cover of 
seagrass due to increased sediment deposition or 

Toxic chemicals 

In general the Western Australian coastal environment 
is not subjected to large-scale inflows of toxic 
chemicals. The 1998 Western Australian State of the 
Environment Report does not consider them a threat”. 
Awareness of toxic, human-produced chemicals and 

Summary of major human-induced declines of seagrass in Western Australia 

Place Seagrass community 
Posidonia sinuosa 
Posidonia australis 
Posidonia australis 
Amphibolis antarctica 

Cockburn Sound, 
Western Australia 
Princess Royal and Oyster Harbours, 
Western Australia 

Extent of loss Cause 
7.2 km’ lost (more than 
two thirds} 

8.1 km? lost [46%] 

Increased epiphytism blocking light 

Decreased light, increased epiphyte 
and drift algal loads 

Source: Cockburn Sound: Cambridge et al.'""), Silberstein et al. ”'; Princess Royal and Oyster Harbours: Walker et al'"*", Wells et al”) 



Photo: D. Walker 


Underwater meadow of Posidonia australis abutting a limestone 
reef, Rottnest Island, Western Australia 

their impacts on marine organisms has increased, and 
such industrial inflows are controlled by Licence 
Conditions from the Western Australia Department of 
Environmental Protection. Urban runoff may include 
such chemicals, but in Western Australia the runoff is 
separated from the sewage system. Some direct runoff 
may still influence groundwater or the coastal 
environment, and increasing population pressure will 
result in increased risk of contamination. 

Fortunately, the aquaculture industry in Western 
Australia has avoided the use of antibiotics in fish 
foodstuffs. The potential effects of antibiotics” may 
result in widespread changes in microbial activities, 
with consequences up the food web, as well as for 
nutrient recycling in coastal sediments. 

The effects of antifouling compounds are also a 
concern. Tributyltin [TBT] has been recorded from 
Western Australian locations’, highest near marinas 
and ports. TBT contamination is present at various 
levels in all major ports in Western Australia. TBT 
contamination is widespread throughout Perth 
Metropolitan marine environment”. The use of TBT has 
been banned in Western Australia on vessels longer 
than 25 m. 

Introduction of exotic (alien) species 

Exotic marine organisms have been introduced to 
Western Australia via ballast water and hull fouling 
from shipping, and threaten natural distributions of 
organisms, including seagrass. It is estimated that 100 

million metric tons of ballast water are discharged into 
this region's marine waters each year. Currently, 
controls are only voluntary. Introduced marine species 
may threaten native marine flora and fauna and human 
uses of marine resources such as fishing and 
aquaculture. Knowledge of species introduced and 
their distribution has recently been updated. The risk of 
damage to marine biodiversity is largely unknown but 
international experience suggests that the potential for 
significant environmental impact is high”. 
Displacement of existing flora and fauna by introduced 
species, intentional or accidental, has been widely 
reported elsewhere’. 

The 1998 Western Australian State of the 
Environment Report estimated that over 27 exotic 
species have been introduced to Western Australia”. 
Twenty-one of these are known to have been introduced 
into Perth Metropolitan waters, the most highly visible 
being a large polychaete worm Sabella spallanzani 
(Sabellidae family). This worm occupied up to 20 ha of 
the seafloor and most of the structures in Cockburn 
Sound, outcompeting the native Posidonia species, but 
its incidence has been declining’. 


Large, mainly monospecific meadows of southern 
Australian endemic species form about one third of the 
habitat in the coastal regions of Western Australia and 
amount to some 20000 km’. The tropical species are 
less abundant but add a further 5000 km’. 


Human utilization of seagrass in Western Australia is 

relatively restricted. Few commercial and recreational 

species are taken from seagrass habitats. According to 
the 1998 Western Australian State of the Environment 

Report’, human activities most affecting coastal 

seagrass habitats in Western Australia are: 

) direct physical damage caused by port and 
industrial development, pipelines, communi- 
cation cables, mining and dredging, mostly in the 
Perth Metropolitan and Pilbara marine regions; 

() excessive loads of nutrients, causing seagrass 
overgrowth and smothering by epiphytes, from 
industrial, domestic and agricultural sources, 
mostly in the Lower West Coast, Perth Metro- 
politan and South West Coast marine regions; 

fo) land-based activity associated with ports, 
industry, aquaculture and farming, mostly in the 
Pilbara, Central West Coast, Lower West Coast, 
Perth Metropolitan and South West Coast marine 

to) direct physical damage caused by recreational 
and commercial boating activities including 
anchor and trawling damage, mostly in the 

Kimberley, Pilbara, Shark Bay, Perth Metro- 
politan and Geographe Bay areas. Trawling nets 
remove sponges and other attached organisms 
from the seafloor. 

The marine environment receives most of the 
surface water from land. The quality of this water is 
affected by activities and the environment of the 
catchments through which it flows. Soil and nutrients 
can be carried by river discharges to coastal waters, 
causing water quality deterioration. Groundwater can 
also carry terrestrial pollution into the marine 
environment. Direct discharges such as sewage and/or 
treated wastewater and industrial outfalls, and 
accidental discharges such as spills and shipping 
accidents, also influence coastal water quality”. 

These land-based activities, their impacts on 
ground and surface water and the ultimate movement 
of these waters into nearshore marine environments 
are the major human influence on the Western 
Australian coast. They result in most pollution of the 
marine environment and the resulting chronic 
degradation of marine habitat. Degradation of the 
marine environment leads to reductions in the area of 
seagrass, as well as corals and mangroves. 

Growing land- and marine-based tourism 
development in Western Australia and the central- 
ization of population growth will cause these impacts to 
increase unless adequate protection and management 
of the coast occurs. 

Fisheries impacts 

Most fishing methods in Western Australia are 
suggested to have a limited effect on the shallow 
coastal environments where seagrasses occur”. 
Methods that may significantly affect the environment, 
for example dredging and pelagic drift gill-netting, are 
banned. Other methods, such as trawling, that alter the 
benthic environment are restricted to prescribed areas. 
Currently, many of these impacts cannot be 
quantified”, but current assessments of the 
sustainability of fisheries practices suggest that 
damage to seagrass beds is minimal. 

At present there are fewer than 100 trawlers 
Operating in a series of discrete managed fisheries 
within the total Western Australian fishing fleet of 
around 2000. The number of these trawl licenses will be 
reduced over time. Areas available to trawling within 
each trawl fishery management area are also restric- 
ted. There are significant demersal gill-netting closures 
in areas of high abundance of vulnerable species such 
as dugong (for example, Shark Bay and Ningaloo Reef). 

Pollution, loss of habitat, sedimentation from 
dredge spoil and agricultural runoff can impact heavily 
on fish stocks, primarily in nearshore waters and 

Western Australia 

estuaries. Nutrient enrichment of some Western 
Australian estuaries continues to be a problem. The 
introduction of exotic marine organisms from ballast 
water and via the aquarium industry remains an area 
of concern. 


Protected areas 

All the marine parks in Western Australia contain 
significant seagrass habitats. In particular the Shark 
Bay World Heritage Property (see Case Study 10.1} 
contains more than 4 000 km’ of seagrass beds of high 
diversity”, as well as a population of more than 10 000 
dugong, and turtles. 

Two marine parks in the Perth area, Marmion and 
Shoalwater Islands, contain about 20 percent seagrass. 
The Swan River has small sections of marine park, 
mainly declared for their migratory bird populations but 
also including areas of the paddleweed, Halophila 
ovalis. Two coral reef areas to the north of Western 
Australia, Ningaloo and Rowley Shoals Marine Parks, 
contain small but relatively diverse seagrass 

populations’. Three areas to be declared as marine 

LS coet Wa acm alo 
aa ry oy .# . = 
Divers airlifting sediment samples from a Posidonia sinuosa 
meadow, Princess Royal Harbour, Western Australia 

parks, Jurien Bay, Cape Leeuwin-Cape Naturaliste and 
Montebellos-Barrow Island, also have diverse seagrass 
ecosystems represented. 

The establishment of the West Australian Marine 
Parks and Reserves Authority, in which marine 
conservation reserves are vested, should help facilitate 
the development of a comprehensive series of 
reserves. This process is, however, slow, and current 

Photo: D. Walker 




Case Study 10.1 

Shark Bay is a large (13000 km’), shallow (<15 m], 

hypersaline environment, dominated by seagrasses. 

Situated on the West Australian coastline, at about 

26°S, it contains the largest reported seagrass 

meadows as well as the most species-rich seagrass 
assemblages. Shark Bay is also a World Heritage 

Property, one of only 11 World Heritage sites in the 

world to have been listed under all four categories 

for nomination: 

) outstanding examples representing the major 
stages of the Earth's evolutionary history; 

fo) outstanding examples representing significant 
ongoing geological processes, biological 
evolution and humans’ interaction with their 
natural environment; 

) superlative natural phenomena, formations or 
features, for instance outstanding examples of 
the most important ecosystems, areas of 
exceptional natural beauty or exceptional 
combinations of natural and cultural 

fo) the most important and significant natural 
habitats where threatened species of animals 
or plants of outstanding universal value still 

issues such as extensive plans for aquaculture 
developments being implemented by another section 
of government (Fisheries) may compromise the 
effectiveness of the Parks Authority. The development 
of marine conservation reserves within Western 
Australia must form part of the framework being 
developed federally for Australia, and it must be 
assessed to see if it provides the necessary 
comprehensiveness, adequacy and representativeness 
for marine conservation to be effective. 


On an urgent basis, more detailed studies of the 
Western Australian marine environment are required if 
a sound basis for management is to be developed, both 
within the marine park and reserve system and outside 
it. There have been few coherent, broad-based studies 
{both in time and space] that have researched the 
cumulative impact of pollution, siltation, habitat 
fragmentation and introductions of invasive species on 
the community structure of marine communities”. 
Further effort is needed on the influence of these 
human activities on the whole community, although it 


Although the area also has terrestrial 
significance, and is home to dolphins, the world’s 
largest stable population of dugongs and living 
stromatolites, the seagrasses are responsible for 
some of the most impressive illustrations in the 
world of the interaction between seagrasses and 
their environment. Shark Bay provides an out- 
standing example of the role that seagrasses can 
play in influencing the physical, chemical and 
biological evolution of a marine environment. 


Shark Bay is a semi-enclosed basin, with restricted 
exchange with the Indian Ocean, situated in an arid 
landscape where evaporation exceeds precipitation 
by a factor of ten. There are two gulfs, the eastern 
and western, formed by pleistocene dunes, creating 
a series of inlets and basins. Astronomical tides are 
less than 1 m, thus atmospheric conditions influence 
water levels. In summer, strong southerly winds 
transport about 1-1.5 m of water northwards out of 
the bay, exposing sand flats up to 2 km wide. There is 
a well-developed salinity gradient developed as the 
marine waters cross the shallow carbonate banks of 
the Faure Sill. Salinities in Hamelin Pool may reach 

will take a long-term commitment to fund these 
multidisciplinary studies. 

A more coherent approach to managing the 
marine environment is required by government 
agencies. Some 15 different government agencies have 
some responsibility for management of the Western 
Australian marine environment. The 1998 State of the 
Environment Report” recommends that the state 
government should establish a formal framework to 
coordinate environmental management within Perth’s 
Metropolitan marine region and between these waters 
and their land catchments. This should be used as a 
pilot program for expansion to other areas under 
pressure from domestic and rural discharges. 

A recent change in state government in Western 
Australia has seen major changes to the structure of 
government departments that may alleviate some of 
the previous problems. 


Diana Walker, School of Plant Biology, University of Western Australia, 
WA 6907, Australia. Tel: +61 (0)8 9380 2089/2214. Fax: +61 (0}8 9380 1001. 
E-mail: diwalker( 


70 psu. Strong tidal currents, up to 8 knots, flow 
through channels in the Faure Sill. 

Seagrasses, particularly the southern 
Australian endemic species Amphibolis antarctica 
and Posidonia australis, dominate the subtidal 
environment, to depths of about 12 m. The intertidal 
flats are composed of mixed Halophila ovalis and 
Halodule unjnervis. The 12 species of seagrass in 
Shark Bay make it one of the most diverse seagrass 
assemblages in the world. Seagrass covers more 
than 4000 km’? of the bay, about 25 percent, with the 
1030-km? Wooramel Seagrass Bank being the 
largest structure of its type in the world. 


The presence of extensive, monospecific beds of 
these large, lengthy [2 m) seagrasses, baffle the 
currents and modify the sediments underlying the 
seagrass. The plants trap and bind the sediments 
accreting from calcareous epiphytes and associated 
epifauna. The plants can significantly slow the rate 
of water movement over the bottom, and stabilize 
the otherwise unstable sediments. Rates of 
sediment accretion associated with Amphibolis 
antarctica are higher than those associated with 
coral reefs. This is related to high rates of leaf 
turnover, depositing more calcareous sediments. 
Over geological time, this had led to the build-up of 

Anon [1994]. Australian National Tide Tables 1995. Australian 
Government Publishing Service, Canberra. 256 pp. 
Anon [1998]. Environment Western Australia 1998: State of the 
Environment Report. Department of Environmental Protection, 
Western Australia. 135 pp. 
Zann LP, Kailola P {eds} [1995]. The State of the Marine 
Environment Report. Technical Annex |. The Marine Environment. 
Zann LP [1996]. The State of the Marine Environment Report for 
Australia. Technical Summary. Department of Environment, Sport 
and Territories, Commonwealth of Australia. 515 pp. 
Searle JD, Logan BW [1978]. A Report on Sedimentation in 
Geographe Bay. Research Project R T 2595. Department of Geology, 
University of Western Australia. Report to Public Works 
Department, Western Australia. 72 pp. 
McMahon K, Young E, Montgomery S, Cosgrove J, Wilshaw J, 
Walker DI [1997]. Status of a shallow seagrass system, Geographe 
Bay, south-western Australia. Journal of the Royal Society of 
Western Australia 80: 255-262. 
Congdon RA, McComb AJ [1979]. Productivity of Ruppia: Seasonal 
changes and dependence on light in an Australian estuary. Aquatic 
Botany 6: 121-132. 
Carruthers TJB, Walker DI, Kendrick GA [1999]. Abundance of 
Ruppia megacarpa Mason in a seasonally variable estuary. 
Estuarine Coastal and Shelf Science 48: 497-509. 
Walker DI [1989]. Seagrass in Shark Bay - the foundations of an 
ecosystem. In: Larkum AWD, McComb AJ, Shepherd SA [eds] 

Western Australia 

banks under the seagrass, forming the Faure Sili, as 
well as the extensive sand flats. 

The build-up of the banks underlying the 
seagrass, in turn, has restricted the circulation of 
oceanic seawater, which with high evaporation and 
low rainfall results in the hypersalinity gradient in 
the inner reaches of the bay. This makes the 
southern areas of Hamelin Pool unsuitable for 
seagrasses, but has allowed the development of 


The waters flowing over the seagrasses are 
depleted in phosphorus by the seagrasses them- 
selves. For Shark Bay as a whole, the seagrass 
meadows represent an enormous pool, with some 
86 million kg of nitrogen and 6 million kg of 
phosphorus being required to support the seagrass 
growth. Only about 10 percent of this can be 
supplied from the oceanic inflow, so the high rates 
of production must be supported by tight recycling, 
both from decomposition in situ and from internal 

Seagrasses in Shark Bay thus represent “an 
outstanding example representing significant on- 
going geological processes, and biological evolu- 
tion”, demonstrating how important seagrasses are 
throughout the world. 

Seagrasses: A Treatise on the Biology of Seagrasses with Special 
Reference to the Australian Region. Elsevier/North Holland, 
Amsterdam. pp 182-210. 

10 Walker DI, Prince RIT [1987]. Distribution and biogeography of 
seagrass species on the north-west coast of Australia. Aquatic 
Botany 29: 19-32. 

11 Walker DI [1997]. Marine Biological Survey of the Central 
Kimberley, Western Australia. Report to the National Estates 
Committee. 159 pp. 

12 Dennison WC, Kirkman H [1996]. Seagrass survival model. In: Kuo 

JJS, Phillips R, Walker DI, Kirkman H leds) Seagrass Biology: 
Proceedings of an International Workshop, Rottnest Island, 
Western Australia, 25-29th January 1996. Faculty of Science, 
University of Western Australia, Perth. pp 341-344. 

13 Kirkman H, Walker DI [1989]. Western Australian seagrass. In: 
Larkum AWD, McComb AJ, Shepherd SA {eds} Biology of 
Seagrasses: A Treatise on the Biology of Seagrasses with Special 
Reference to the Australian Region. Elsevier/North Holland, 
Amsterdam. pp 157-181. 

14 Cambridge ML [1980]. Ecological Studies on Seagrass of South 
Western Australia with particular reference to Cockburn Sound. 
PhD thesis, University of Western Australia, Perth. 326 pp. 

15 Hillman K, Walker DI, McComb AJ, Larkum AWD [1989]. 

Productivity and nutrient limitation. In: Larkum AWD, McComb AJ, 

Shepherd SA (eds) Seagrasses: A Treatise on the Biology of 
Seagrasses with Special Reference to the Australian Region. 
Elsevier/North Holland, Amsterdam. pp 635-685. 










Dennison WC, Orth RJ, Moore KA, Stevenson JC, Carter V, Dollar S, 
Bergstrom PW, Batiuk RA [1993]. Assessing water quality with 
submersed aquatic vegetation. Bioscience 43: 86-94. 

Kirk JTO [1994]. Light and Photosynthesis in Aquatic Ecosystems. 
Cambridge University Press, Cambridge. 

Walker DI, McComb AJ [1992]. Seagrass degradation in Australian 
coastal waters. Marine Pollution Bulletin 25: 191-195. 

Cambridge ML, Chiffings AW, Brittan C, Moore L, McComb AJ 
[1986]. The loss of seagrass in Cockburn Sound, Western Australia. 

Il. Possible causes of seagrass decline. Aquatic Botany 24: 269-285. 

Lord DA [1994]. Coastal eutrophication: Prevention is better than 
cure. The Perth Coastal Water Study 45: 22-27. 

Lukatelich RJ, McComb AJ [1989]. Seasonal Changes in 
Macrophyte Abundance and Composition in a Shallow 
Southwestern Australian Estuarine System. Waterways 
Commission, Perth, Western Australia. 

Lukatelich RJ, McComb AJ [1986]. Distribution and abundance of 
benthic microalgae in a shallow southwestern Australian estuarine 
system. Marine Ecology Progress Series 27: 287-297. 

Lavery PS, Lukatelich RJ, McComb AJ [1991]. Changes in the 
biomass and species composition of macroalgae in a eutrophic 
estuary. Estuarine Coastal and Shelf Science 33: 1-22. 

McMahon K, Walker DI [1998]. Fate of seasonal, terrestrial nutrient 
inputs to a shallow seagrass dominated embayment. Estuarine 
Coastal and Shelf Science 46: 15-25. 

Bastyan G [1986]. Distribution of Seagrasses in Princess Royal 
Harbour and Oyster Harbour on the Southern Coast of Western 
Australia. Technical Series 1. Department of Conservation and 
Environment, Perth, Western Australia. 50 pp. 

Walker DI, Hutchings PA, Wells FE [1991]. Seagrass, sediment and 
infauna - a comparison of Posidonia australis, Posidonia sinuosa 
and Amphibolis antarctica, Princess Royal Harbour, South-Western 
Australia |. Seagrass biomass, productivity and contribution to 
sediments. In: Wells FE, Walker DI, Kirkman H, Lethbridge R {eds} 
Proceedings of the 3rd International Marine Biological Workshop: 
The Flora and Fauna of Albany, Western Australia. Vol 2. Western 
Australia Museum. pp 597-610. 










Wells FE, Walker DI, Hutchings PA [1991]. Seagrass, sediment and 
infauna - a comparison of Posidonia australis, Posidonia sinuosa 
and Amphibolis antarctica in Princess Royal Harbour, South- 
Western Australia Ill. Consequences of seagrass loss. In: Wells FE, 
Walker DI, Kirkman H, Lethbridge R leds] Proceedings of the 3rd 
International Marine Biological Workshop: The Flora and Fauna of 
Albany, Western Australia. Vol 2. Western Australian Museum. pp 

Chiffings AW, McComb AJ [1981]. Boundaries in phytoplankton 
populations. Proceedings of the Ecological Society of Australia 11: 

Silberstein K, Chiffings AW, McComb AJ [1986]. The loss of 
seagrass in Cockburn Sound, Western Australia. Ill. The effect of 
epiphytes on productivity of Posidonia australis Hook. f. Aquatic 
Botany 24: 355-371. 

Kendrick GA [1991]. Recruitment of coralline crusts and 
filamentous turf algae in the Galapagos archipelago: Effect of 
stimulated scour, erosion and accretion. Journal of Experimental 
Marine Biology and Ecology 147: 47-63. 

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Concentration and persistence of oxytetracycline in sediments 
under a marine salmon farm. Aquaculture 123(1-2): 31-42. 

Kerry J, Hiney M, Coyne R, Cazabon D, Nicgabhainn S, Smith P 
{1994]. Frequency and distribution of resistance to oxytetracycline 
in micro-organisms isolated from marine fish farm sediments 
following therapeutic use of oxytetracycline. Aquaculture 123(1-2): 

Kohn AJ, Almasi KN [1993]. Imposex in Australian Conus. Journal 
of Marine Biology Association UK 73: 241-244. 

Sindermann CJ [1991]. Case histories of effects of transfers and 
introductions on marine resources - Introduction. Journal du 
Conseil 47: 377-378. 

Chaplin G, Evans DR [1995]. The Status of the Introduced Marine 
Fanworm Sabella spallanzanii in Western Australia: A Preliminary 
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34 pp. 

Regional map: Australasia 




Wy OOS 002 








A manatee (Trichechus manatus], feixe-boi in Portugese, 
over a Halodule wrightii bed in Recife, Brazil 

A sea horse, Hippocampus whitei, amongst Zostera capricorni in Sydney 

Harbour, Australia 

Photo: J. Harmelin 

to: F.T. Short 


Mediterranean Posidonia oceanica seagrass beds with 
saupe (Sarpa sarpa) and bream [Diplodus spp.) 

Sea star in Enhalus acoroides and 

Snails grazing epiphytes on Zostera 
Thalassia hemprichii, Micronesia 

Photo: F.T. Sho 

marina blades in southern Norway. 

King helmet in Thalassia : 
testudinum, Turks & Caicos Lizard fish in Amphibolis antarctica, Western Australia 

11 The seagrasses of 

Eastern Australia 


eastern Australian coastline which extends from 

the tropics (10°S) to the cool temperate zone 
(44°S) and includes the Great Barrier Reef World 
Heritage Area. The area includes the Gulf of Carpentaria 
to the north and around the coastline of Australia to 
Tasmania and to Spencer Gulf. There are extensive 
seagrass habitats in this region including tropical and 
temperate seagrass assemblages. An overlap between 
these two zones occurs in Moreton Bay, southern 
Queensland". Both tropical and temperate species in 
Australia are mostly found growing in water less than 10 
m below mean sea level”. Some species of tropical 
Halophila can be found to depths of 60 m". 

The eastern Australian coast includes areas of 
diverse physical characteristics. The tropical north 
coast and Gulf of Carpentaria are monsoon influenced, 
mostly with muddy sediments, low human population 
and low levels of disturbance. The tropical and most of 
the temperate subtropical Queensland east coast is 
sheltered by the Great Barrier Reef and is effectively a 
long lagoon. The temperate east and south coasts are 
sandier and more exposed and include the large [by 
Australian standards) population centers of Brisbane, 
Sydney, Melbourne and Adelaide with a standard suite 
of associated anthropogenic coastal disturbances. 

The highest species diversity of seagrass is found 
near the tip of Cape York in the very north, with a 
gradual decline in diversity moving south down the 
east coast'!. This is thought to be a result of geo- 
graphic distance from a center of diversity in the 
Malaysian/Indonesian region driven by the east 
Australian current which runs roughly north to south”, 
combined with changes in temperature, topography 
{available substrate), past changes in sea level and 
exposure to wave action". 

The temperate species in the southern half of the 
region include members of the genera Amphibolis, 
Posidonia and Zostera which are found predominately in 

Seen meadows are a prominent feature of the 

R. Coles 
L. McKenzie 
S. Campbell 

sheltered estuaries and bays. Amphibolis is an 
Australian endemic. They possibly had a much wider 
distribution in the early Paleocene (64 million years ago) 
with rapid climatic and tectonic changes since that time 
restricting their distribution to southern Australia’. 
Posidonia has a fractured distribution at the present 
time (southern Australia and the Mediterranean], also 
likely to be the result of localized extinctions in the 
past”. The genus Zostera has both temperate and 
tropical species in Australia. 

The tropical meadows are highly diverse, but 
generally have lower biomass than those in temperate 
parts. While bays such as Hervey Bay and Moreton Bay 
have large areas of seagrass, most tropical seagrasses 
are found in the intertidal or shallow subtidal environ- 
ments of the Gulf of Carpentaria and the central and 
southern Great Barrier Reef World Heritage Area 
lagoon with extension into deeper waters in the central 
and northern sections. 

The importance of seagrass meadows as struc- 
tural components of coastal ecosystems has resulted 
in research interest being focused on the biology and 
ecology of seagrasses and on the methods for mapping, 
monitoring and protection of critical seagrass habitats. 
Seagrasses of eastern Australia are important for 
stabilizing coastal sediments, providing food and 
shelter for diverse organisms, as a nursery ground for 
shrimp and fish of commercial importance, and for 
nutrient trapping and recycling”. In eastern Australia 
the marine mammal, Dugong dugon, and the green sea 
turtle, Chelonia mydas, feed directly on seagrasses. 
Both animals are used by traditional Australian 
communities for food and ceremonial use. Both species 
have declined in number, and protection of their habitat 
and food source Is vital. 

The extent of seagrass areas and the ecosystem 
values of seagrasses are the basic information required 
for coastal zone managers to aid planning and 
development decisions that will minimize impacts on 





seagrass habitat. In general, our knowledge of intertidal 
and shallow subtidal {down to 10 m]) distributions is 
good; however, we have only a basic understanding of 
deepwater (>10 m] seagrasses throughout the region. It 
is important to document seagrass species diversity and 
distribution and identify areas requiring conservation 
measures before significant areas and species are lost. 


Gulf of Carpentaria and Torres Strait 

The Gulf of Carpentaria is a large, shallow, muddy 
marine bay. Extensive open coastline seagrass 
communities, mainly of the genera Halodule and 
Halophila intertidally, and Syringodium and Cymodocea 
subtidally, are found along the southern and western 
sides of the gulf”. Along the exposed eastern coast of 
the gulf, seagrasses are generally sparse and 
restricted to the leeside of islands, protected reef flats, 
and estuaries and protected bays. The coastline of the 
eastern gulf is extremely shallow and regularly 
disturbed by prevailing winds. Sediments throughout 
the gulf are predominately fine muds, and these are 
easily resuspended due to the shallow bathymetry 
resulting in increased turbidity, which restricts 
seagrass distribution and growth. Reef flat communi- 
ties are dominated by Thalassia. Meadows in estuaries 
and sheltered bays are mostly of the genera Halodule, 
with Cymodocea and Enhalus. 

The Torres Strait is a shallow (mostly 10-20 m 
depth) body of water 100 km long and 250-260 km 
wide [east-west], formed by a drowned land ridge 
extending from Cape York to Papua New Guinea. The 
area has a large number of islands, shoals and reefs. 
Reefs are generally aligned east-west, streamlined 
by the high-velocity tidal currents that pour through 
the inter-reef channels. Seagrass communities occur 
across the open seafloor, on reef flats and subtidally 
adjacent to continental islands. A well-defined line of 
large reefs runs northwards from Cape York, 
including the Warrior Reefs with extensive seagrass- 
covered reef flats. Mixed species occur on these flats, 
most commonly of the genera Halodule, Thalassia, 
Thalassodendron and Cymodocea. The large ex- 
panses of open water bottom are covered with either 
sparsely distributed Halophila or mixed species 
(Halodule, Thalassia and Syringodium) communities. 
Lush Halophila ovalis and Halophila spinulosa 
communities are also found in the deep waters 
(>30 m) of the southwestern Torres Strait. 

Northeast coast 

Tropical seagrass habitats in northeastern Australia 
are extensive, diverse and important for primary and 
secondary production’. A high diversity of seagrass 
habitats is provided by extensive bays, estuaries, rivers 

and the 2600-km Great Barrier Reef with its reef 
platforms and inshore lagoon. 

Carruthers et al." classified the northeast coast 
seagrass systems into river estuaries, coastal, 
deepwater and reef habitats. All but some of the reef 
habitats are significantly influenced by seasonal and 
episodic pulses of sediment-laden, nutrient-rich river 
flows, resulting from high-volume summer rainfall. 
Cyclones, severe storms and wind waves, as well as 
macrograzers (dugongs and turtles) influence all 
habitats in this region to varying degrees. The result is 
a series of dynamic, spatially and temporally variable 
seagrass meadows. 

River estuary habitats include a wide range of 
subtidal or intertidal species and can be highly 
productive. The species mixture, growth and distri- 
bution of these seagrass meadows are influenced by 
terrigenous runoff as well as temperature and salinity 
fluctuations. Increased river flows in summer cause 
higher sediment loads and reduced light, creating 
potential light limitation for seagrass. Associated 
erosion and unstable sediments make river and inlet 
habitats a seasonally stressful environment for 
seagrass growth. These meadows often have high 
shoot densities but low species diversity”. Differences 
in life history strategies, resilience to habitat variability, 
and the physical characteristics of the inlet act to 
control species assemblages in different river and inlet 

Coastal habitats also have extensive intertidal 
and subtidal seagrasses. Intertidal environments are 
impacted by sediment deposition, erosion, tidal 
fluctuations, desiccation, fluctuating and sometimes 
very high temperature, and variable salinity”. Tidal 
range can be as large as 6 m. These communities are 
affected rapidly by increased runoff with heavy rain or 
cyclone events'', but a large and variable seed bank 
can facilitate recovery following disturbance’. Inshore 
seagrass communities are found in varying quantity 
along the eastern Queensland coastline, mostly where 
they are protected from the prevalent southeast winds 
by the Great Barrier Reef. Along the southern 
Queensland coast, the Great Barrier Reef offers little 
protection and coastal seagrass meadows are 
restricted to sheltered bays, behind headlands and in 
the lee of islands. Extensive coastal seagrass meadows 
occur in north-facing bays such as Moreton Bay, Hervey 
Bay and Shoalwater Bay. 

Increasing distance from the coast decreases the 
impacts from pulsed terrigenous runoff, and in these 
regions clear inter-reef water at depth (>15 m] allows 
for deepwater seagrass growth. Throughout the Great 
Barrier Reef region, approximately 40000 km? of 
lagoon and inter-reef area has at least some seagrass, 
most of low density (<5 percent cover)”. 

Deepwater seagrass areas are dominated by 
species of Halophila®*"*. Large monospecific mead- 
ows of seagrass occur in this habitat composed mainly 
of Halophila decipiens or Halophila_ spinulosa. 
Halophila spp. display morphological, physiological and 
life history adaptations to survival in low-light environ- 
ments. Halophila spp. can be annuals in the Great 
Barrier Reef region, have rapid growth rates and are 
considered to be pioneering species'’”. An important 
characteristic of this strategy is high seed production. 
Rates of 70000 seeds/m*/year have been estimated 
from field observations of Halophila tricostata"”. 

The distribution of deepwater seagrasses 
appears to be mainly influenced by water clarity and a 
combination of propagule dispersal, nutrient supply 
and current stress. High-density deepwater sea- 
grasses occur mostly on the inner shelf in the central 
narrow-shelf section of the east coast which 
experiences a moderate tidal range and is adjacent to 
high-rainfall rainforest catchments. Where there are 
large tidal ranges, just to the south of Mackay, no major 
deepwater seagrass areas exist, but some meadows 
occur further south in Hervey Bay where tide ranges 
moderate again’. Deepwater seagrasses are uncom- 
mon north of Princess Charlotte Bay, a remote area of 
low human population and little disturbance. This may 
be the result of the east Australian current diverging at 
Princess Charlotte Bay and the far northern section 
may not receive propagules for colonization from 
southern meadows. Much of this coast is also silica 
sand and low in rainfall and stream runoff, and it is 
possible that limited availability of nutrients restricts 
seagrass growth”. 

Reef seagrass communities support a high 
biodiversity and can be extensive and highly productive. 
Shallow unstable sediment and fluctuating tempera- 
ture characterize these habitats. Low nutrient availa- 
bility is a feature of reef habitats, and seagrasses are 
likely to be nitrogen limited'”. Seagrasses are more 
likely to be present on reefs with vegetated cays than on 
younger reefs with highly mobile sand. Intermittent 
sources of nutrients arrive when seasonal runoff 
reaches the reef. In some localized areas, particularly 
coral cays, seabirds can add high amounts of 
phosphorus to reef environments. The more successful 
seagrass species in reef habitats of the Great Barrier 
Reef include Thalassia hemprichii, Cymodocea 
rotundata, Thalassodendron ciliatum, the colonizing 
species Halophila ovalis, and species of the genus 

New South Wales, Victoria and Tasmania 

Ten species of seagrass (excluding Lepilaena cylindro- 
carpa) are recorded in this region’. Species of the 
genus Zostera (including the former Heterozostera) are 

Eastern Australia 

Torres* Strait 
Cape York 

Gulf of 
Carpentaria CORAL SEA 

Green Island 

Great Barrier Reef 
« World Heritage Area 



Deception Bay’ 
Brisbane, & 


30° S 

Port Macquarie » 

Tom, f 
, Zs Sydney ¢ Botany Bay 
x N Adelaide 2 

Spencer 9° . 
Gulf Victoria 

, Melbourne » y 

oP Rig 

Port Hacking > — Westernport Bay 
Bass Sirait 

Port Phillip Bay a 




Coorong Mallacoota 


® Freycinet 
600 Kilometers Hi 

Bnuny Island 

Map 11.1 
Eastern Australia 

the most common as they dominate in estuaries and 
coastal lagoons". In Victoria and Tasmania, Posidonia 
and Amphibolis are also found, mainly near estuary 
entrances, or in sheltered bays adjacent to Bass Strait 

The distribution and occurrence of seagrasses 
depends on the estuary type, i.e. drowned river valley, 
barrier estuary or coastal lagoon'"'. Seagrass species 
composition and distribution is associated mostly with 
sediment type and with differing exposure to wave 
energy from the open ocean. Seagrasses are generally 
more abundant several kilometers upstream from the 
estuary entrance due to lesser tidal and wave 
disturbance. Seagrasses in coastal lagoons may also be 
affected by the frequency with which the lagoon 
entrance is open to the ocean or closed by shifting sand 
banks, changing conditions from brackish to saline. 
Agricultural development and poor catchment practices 
in some regions have resulted in high sediment and 
nutrient loads reducing light availability and favoring 
species which can tolerate lower light levels. In other 
localities, reduced freshwater flows (due to industrial 
and agricultural extraction) have increased salinities. 

In protected sites, mixed stands of Zostera 






tasmanica, Zostera capricorni (formerly Zostera 
muelleri) and Halophila ovalis dominate. Ruppia 
meadows are common in areas of high freshwater 
input. A feature of estuarine habitats in this region is 
heavy winter-spring rains with associated high turbidity, 
followed by high salinity and low rainfall in summer. 

In less-protected areas dominated by sandy 
sediments [e.g. north coast of Tasmania, Bass Strait 
islands) mixed seagrass communities consist of larger, 
slower growing species such as Posidonia australis, with 
small, faster growing species such as Zostera tasmanica 
and Halophila ovalis occupying the gaps between 
meadows and areas close to freshwater inputs. At the 
mouth of some bays and in areas dominated by sandy 
siliceous sediments and exposed to ocean swells in 
Victoria, the slow-growing seagrass Amphibolis 
antarctica (Amphibolis griffithii fills the same role in 
South Australia) forms patches of varying sizes rather 
than extensive monospecific meadows. In these areas, 
nutrient inputs are low and sediments are nutrient poor. 

Large oceanic bays in southeast Tasmania have 
meadows of Halophila and Zostera species. Seagrass 
distribution is influenced by biogeography and geo- 
morphology as well as wave energy. Deep, oceanic 
seagrass beds of Posidonia australis and Amphibolis 
antarctica are also present to depths of 22 m in clear 
non-polluted water. Their distributions are influenced by 
depth, bottom type, wave energy and geomorphology. 
Most seagrasses in southeastern Australia are restric- 
ted to depths of less than 20 m by light availability. 

South gulf coast of South Australia 
Seagrass distribution in South Australia is dependent 
on coastal topography, bathymetry and environment”. 

.The most extensive meadows are found in the large 

expanses of sheltered shallow water in Spencer Gulf 
and Gulf St Vincent. These are predominantly Posidonia 
and Amphibolis meadows, with Halophila and Zostera 
species. Large seagrass meadows which are 
dominated by species of Zostera also occur along the 
southeastern coast of South Australia in coastal 
lagoons [e.g. Lake Alexandrina and Lake Albert). 


Australia has had a relatively stable climate with the 
northward movement of the continent compensating 
during past episodes of global cooling. The biomass 
and diversity of seagrass seen today is most likely to 
have remained relatively unchanged on a continental 
scale for tens of millions of years. 

Agriculture and coastal development started in 
Australia with the arrival of European migrants only 
200 years ago and coastal influences on seagrass 
before that date would have been almost entirely 
natural. Sediment and nutrient loads to estuaries and 


enclosed waters such as Moreton Bay and Westernport 
Bay have undoubtedly influenced the modern 
distribution of seagrasses, particularly in temperate 
waters. Less easy to determine is the likely effect in 
tropical waters where turbidities are already naturally 
high. Dramatic declines in grazer populations [turtle 
and dugong) from increased hunting would be expected 
to allow an increase in seagrass, particularly of 
biomass where climax communities can now develop. 

Traditionally, the fruit of Enhalus acoroides was 
eaten in the northern islands and the leaf fibers were 
possibly used to make nets and cord. This use was 
likely to have been infrequent and of low importance to 
seagrass distribution as the human population was 
very small before European migration. Seagrasses 
were used to make matting and for bed mattresses 
during the Second World War. They were also used for 
fertilizer, such as in Lacepede Bay in southeastern 
South Australia, where Posidonia angustifolia leaf drift 
and wrack is still harvested from the beach for soil 
conditioner and compost mixes”. Such activities are 
now illegal in many parts of Australia where both live 
and dead seagrasses are protected. 

There are reports from the southern and eastern 
Australian coastline that seagrass communities have 
declined in recent decades’. Anecdotal reports of 30 
years ago from residents in the Hervey Bay and Great 
Sandy Strait region describe large long-leaved (>30 cm) 
Zostera capricorni meadows abundant over the 
intertidal banks. Long-time residents report abundant 
fishing and bird life [especially black swans) and say 
that the seagrass wrack was so plentiful that it was 
harvested from the beaches for garden mulch. Today, 
much of the seagrass on the intertidal banks in the 
region is sparse or low-cover Zostera capricorni with 
short [<10 cm) and narrow leaves. Fishing is reported 
to have declined and black swans no longer frequent 
the region. Unfortunately, accurate mapping programs 
were not instigated until the late 1980s so these types 
of report are impossible to verify and may well be 

In Victoria there are unquantified reports of 
Zostera loss in Westernport Bay during the 1950s. The 
decline coincided with a reduction in fish catches. 
Anecdotal reports and photographs from local 
residents in the north and eastern regions of 
Westernport Bay, prior to the loss of seagrasses, 
describe “lush seagrass meadows”. Similarly in Corner 
Inlet, Victoria, a decline in Posidonia australis in the 
1960s was followed by a reduction in fishermen 

operating in the region””. 

More than 450 km’ of seagrass have been lost from 
Australian coastal waters in recent years, largely 

attributed to eutrophication, natural storm events, and 
reductions in available light due to coastal 
development. It is worth noting that there is a high 
probability of bias towards reporting decline, and that 
increases in biomass and area are often not reported. 

There have been several well-documented cases 
of seagrass loss in eastern Australia over the past 50 
years”. In Port Macquarie (New South Wales] 11.3 km? 
of seagrass was lost between 1953 and 1985 due to 
increased turbidity from human activity, resulting in 
declining fish stocks’. Similarly in Botany Bay, a loss 
of 2.5 km’ of Posidona sinuosa, representing 58 percent 
of the bay’s seagrass, was lost between 1942 and 
1986, a consequence of dredging activities and 

In South Australia there has been a significant 
decline in seagrasses on the eastern side of Gulf St 
Vincent due to sewage effluent. Approximately 60 km? 
of Posidona sinuosa and Ampbhibolis antarctica 
meadows were lost between 1935 and 1987! In 
Spencer Gulf, fishermen and local residents have 
reported widespread loss of Amphibolis close to the 
intertidal zone. Recent loss (1992-93) of mixed 
meadows of Posidonia australis, Zostera tasmanica 
and Zostera capricorni were due to sediment accretion 
and desiccation caused by exposure to high air 
temperatures and low humidity”. 

In Victoria, the recorded loss of seagrass has 
been from the large marine bays of Westernport Bay, 
Port Phillip Bay and Gippsland Lakes. In Westernport 
Bay, persistent high turbidity and poor water quality 
due to agricultural runoff, sediment inputs and 
resuspension of sediments caused seagrass to decline 
from 196 km? in the early 1970s to 67 km’ in 1984'”. 
Seagrass recovery has occurred (154 km? by 2001)'", 
but seagrass meadows have failed to recolonize the 
intertidal mud flats in north and western regions and in 
some areas seagrass meadows have at least 45 percent 
lower biomass compared to 25 years ago”. A near 
complete loss of seagrass (ca 31 km’] in the Gippsland 
Lakes from the 1920s to 1950s coincided with reduced 
commercial fish catches”. More recent estimates of 
seagrass abundance suggest that there has been little 
decline over the past 30 years®" except for some 
localized replacement by algae. Similarly, in Port 
Phillip Bay, little change in seagrass area was recorded 
from 1957 (76 km’) to 1981 (96 km’)°**". From 1981 to 
2000, the area of seagrass in Port Phillip Bay declined 
from 96 km? to 68 km’, possibly due to increased 
turbidity and eutrophication in Corio Bay and Swan Bay 
(early 1990s) in the west and southwest of Port Phillip, 
respectively. Drifting algal communities have replaced 
some areas of seagrass vegetation. 

In Queensland, declines of seagrass area resulted 
from flooding and sedimentation. In Moreton Bay, 

Eastern Australia 

thousands of hectares of seagrass, which were present 
prior to the 1980s, have been destroyed by the effects of 
canal estate development. Deception Bay seagrasses 
have declined since 1996 in what may be a cyclic 
pattern. Both cases were due to low light and poor 

Rob Coles visually estimating seagrass abundance and mapping 
distribution (using differential GPS], Shoalwater Bay, Queensland 

water quality associated with urban development and 
possibly agriculture’. Loss from climatic events 
(storms, flooding and cyclones] has occurred in a 
number of regions including Hervey Bay (1000 km? and 
27.75 km’ in separate events in the 1990s) and 
Townsville. Anecdotal evidence and evidence collected 
during lobster fishery surveys suggests that thousands 
of hectares have been lost in the northwest Torres 
Strait due to flooding and sedimentation from Papua 
New Guinea, but these are remote locations and 
difficult to track effectively. 

In northeastern Australia, most seagrass losses 
have been followed by significant recovery. For 
example, approximately 1000 km’ of seagrasses in 
Hervey Bay were lost in 1992 after two major floods and 
a cyclone within a three-week period added to 
pressures on the system from agricultural 
development and land development associated with 
increases in human populations'. The deepwater 
seagrasses died, apparently from light deprivation 
caused by a persistent plume of turbid water from the 
floods and the resuspension of sediments caused by 
the cyclonic seas. The heavy seas uprooted shallow- 
water and intertidal seagrass. Recovery of subtidal 
seagrass [at depth >5 m) began within two years of the 
initial loss'“’, but recovery of intertidal seagrasses was 
much slower. These seagrasses only started to recover 
after four to five years and did not fully recover until 
December 1998". 

The capacity of tropical seagrasses to recover 
appears to be a consequence of morphological, 

% Ww Ww 
= A 4 
SH] YG y 


Photo: L. McKenzie, DPI 




physiological and life history adaptations; the plants can 
be fairly resilient in unstable environments. Halodule 
uninervis and Halophila ovalis are considered pioneer 
species, growing rapidly and surviving well in unstable 
or depositional environments'”:'”. Halophila tricostata 
is an annual, only appearing in late September through 
to February and being sustained by a sizeable seed 
bank". Cymodocea serrulata occurs in deeper 
sediments and has been linked to increased rates of 

Case Study 11.1 


Seagrasses in waters deeper than 15 m in the Great 
Barrier Reef World Heritage Area were surveyed 
between 1994 and 1999. A real-time video camera 
and dredge were towed for four to six minutes on 
1 426 sites to record bottom-habitat characteristics 
and seagrasses. In conjunction with the camera tow, 
a sled-net sample of benthos and a grab sample of 
the sediment were collected. 

Sampling included the Great Barrier Reef 
province from the tip of Cape York Peninsula at 10°S 
to approximately 25°S, or 1000 nautical miles of 
coastline. Sites were located from inshore out to the 

Probability of 
seagrass occurrence 


Probability of occurrence of deepwater seagrasses in the Great 
Barrier Reef Lagoon (contours obtained by spatial smoothing). 

sediment accretion”. Zostera capricorni meadows 

were found to recolonize through vegetative growth and 
can therefore survive small-scale disturbances”. 
Queensland's east and gulf coasts have areas 
where seagrass meadows have expanded. Little is 
known about long-term cycles in seagrass meadow 
size and biomass. The losses and gains being 
measured may fall within a natural range. In heavily 
grazed coastal waters with high dugong and green 


reef edge up to 120 km from the coast. Seagrass 
presence, species and biomass were recorded with 
depth, sediment, Sechii disk depth, associations 
with algae and epibenthos, and proximity to reefs. 

Five seagrasses were present, all from the 
genus Halophila, in depths down to 60 m. Sea- 
grasses were present at 33 percent of sites 
sampled. The species Halophila ovalis, Halophila 
spinulosa, Halophila decipiens, Halophila tricostata 
and Halophila capricorni were found. Halophila 
tricostata is a species endemic to northern 
Australia and Halophila capricorni is found only in 
the southern Indo-Pacific. All other species are 
broadly distributed throughout the Indo-Pacific 
region”. Most seagrass seen in video tows was of 
low density {<5 percent cover] and biomass ranged 
from less than 1 g to 45 g dry weight/m’ (the highest 
was recorded from a Halophila spinulosa-dominant 
meadow in 21 mJ]. Mean biomass was 3.26 +0.36 g 
dry weight/m’. 

The map of seagrass was generated using 
generalized additive models incorporating Loess 
smoothers'”. The degree of smoothness was 
minimized but sufficient to account for both spatial 
effects and spatial correlation. The location of the 
data points was recoded based on the proportion of 
the distance the point was located between the coast 
and the outer edge and the proportion from 10°S to 
the southern edge. The model estimated that as 
much as 40000 km? of lagoon and inter-reef area 
may have at least some seagrass”. This type of map 
or statement of probability is necessary when 
factors such as depth make it impossible to plot 
around the edge of the meadow even if that could be 
defined. With areas of very low biomass and very 
large areas with patchy seagrass, the concept of a 
defined meadow is not always appropriate. Using 
probability to estimate the likelihood of seagrass 
presence must be explained with care as the 

turtle populations, increases in meadow size and 
biomass may reflect simply changes (decreases) in 
herbivore populations and be an indicator of 
disturbance rather than a positive measure. 


Gulf of Carpentaria and Torres Strait 
Approximately 779 km’ of seagrass in the western Gulf 
of Carpentaria were mapped in 1984. In 1986, 

outcome may be scale dependent and the outcome 
is definitely not a “map” in the sense it is normally 
used. If you define the sampling unit as the entire 
Great Barrier Reef Region, the probability of finding 
seagrass in that sampling unit will be 100 percent. A 
smaller unit will have a lower probability. Typically 
the ability of a map drawn this way can be improved 
if physical factors such as light and bottom-type 
location can be incorporated in the model. 

Deepwater seagrasses were most common in the 
central narrow shelf regions which experience a 
moderate tidal range and are adjacent to high- 
rainfall rainforest catchments. Highest densities 
occurred between Princess Charlotte Bay and 
Cairns, and south of 23°S. Halophila tricostata was 
found only between Princess Charlotte Bay and 
Mackay. Other species were spread throughout. 
Seagrasses (Halophila ovalis, Halophila spinulosa, 
Halophila decipiens and Halophila capricorni) 
occurred to 60 m depth. The frequency of occurrence 
of seagrasses declined below 35 m. Halophila 
decipiens was the most commonly found species at 
all depths. Dense algae beds (mainly Caulerpa and 
Halimeda) were found on the outer shelf north of 
Cooktown. Where there are large tidal velocities and 
ranges [4-6 m tidal range], just to the south of 
Mackay, no major deepwater seagrass areas occur. 
Some seagrass habitats were apparent further 
south in Hervey Bay where tidal ranges moderate. 
The ecological role of inter-reef seagrasses 
and algae is not well understood. Some deepwater 
meadows [<25 m] of Halophila ovalis and Halophila 
spinulosa are important dugong feeding habitat. 
Commercial fish and crustacean species were 
uncommon in deep water compared to catches in 
coastal intertidal and shallow subtidal meadows”. 
This seagrass and benthic community 
information is one of the major databases 
supporting development of a multi-use marine park 
plan for maintaining the biodiversity of the Great 
Barrier Reef World Heritage Area based on the 

Eastern Australia 

Queensland Department of Primary Industries (QDPI) 
mapped 184 km’ in the eastern gulf®” and 225 km? 
around the Wellesley Island Group {southern gulf) in 

Using probability models and ground-truthing, 
the Torres Strait is estimated to contain 13425 km‘? of 
seagrass habitat on reef platforms and non-reef soft 
bottoms’ *, much of which is valuable habitat for 
juvenile commercial shrimp. 

BB Halophila decipiens 
35 Halophila spinulosa 
©) Halophila ovalis 
— GBB Halophila tricostata. — 
Halophila capricorni 
WB Seagrass present —— 

Frequency of occurrence (%] 

15-25 25-35 35-45 45-55 55-65 
Depth strata (m) 

Frequency of probability of occurrence (percent adjusted for 
sampling frequency) of seagrasses within each depth stratum. 

Note: Seagrass present = all species combined lincluding 

principles of comprehensiveness, adequacy, and 
representativeness. This “representative areas” 
program has used two processes: a data-based 
statistical approach and a delphic expert 
experience-based questionnaire approach. Thirty- 
eight relatively homogeneous inter-reef bioregions 
have been identified based on the presence and 
distribution of seagrasses, algae, other benthos, 
sediment and habitat descriptions. This information 
will be used to select areas to protect in “no-take” 
zones and to minimize the loss of economic use of 
reef areas by the tourist and fishing industries and 
by recreational users. The deepwater seagrass and 
epibenthos mapping is an excellent example of 
seagrass maps being used directly to support good 
management decisions. 

Source: Coles et al."! 



SE OEE .-—0—_—0—0_.0.0—_—___ —eoeoaOrcvV138”Tnw —— 

Northeast coast 

The northeastern Australia coastline is either within 
the Great Barrier Reef World Heritage Area with high 
conservation values or includes coastline with sea- 
grass meadows supporting valuable shrimp fisheries, 
green turtle or dugong populations. The perceived 
importance of seagrasses in these regions, as well as 
concern about the downstream effects of agriculture, 
effects of fishing and the possibility of shipping 
accidents! have led to an extensive mapping program. 
Broad-scale surveys conducted between 1984 and 1989 
mapped seagrass habitats down to 15 m depth in 
estuaries, shallow coastal bays and inlets, on some 
fringing reefs, barrier reef platforms, inner reef and 
Great Barrier Reef Lagoon". Since 1989 there have 
been repeated surveys at finer scales of resolution in 
certain localities as a result of specific issues (e.g. port 
developments, dugong protection areas]. Some studies 
have repeated surveys at a locality once or twice yearly 

for up to four or more years””. 

Case Study 11.2 

Westernport Bay is a large estuarine tidal bay in 
southern Victoria. It encloses two large islands and 
has an area of 680 km’ of which 270 km’ is intertidal 
mud flat. Intersecting the mud flats is a series of 
complex channels where sediment movement Is 
influenced by the water movement patterns in a net 
clockwise direction. 

Westernport Bay is an area of high biological 
diversity because of its wide range of habitats, 
including seagrass meadows, mangroves, salt 
marsh and deepwater channels. It is an inter- 
nationally significant coastal wetland acknowledged 
by nomination to the Ramsar Convention on 
Wetlands. The bay consists of extensive intertidal 
seagrass meadows, subtidal meadows and macro- 
algal communities. The dominant seagrasses are 
Zostera tasmanica and Zostera capricorni. The 
dominant macroalga associated with seagrass is 
Caulerpa cactoides, which, with other algae, 
comprises about 16 percent of the total marine 

The catchment to the north of Westernport Bay 
was cleared of vegetation in the late 1800s for 
agriculture, and the bay is now subject to inputs of 
nutrients and suspended particulates! Change in 
seagrass distribution from 1956 to 2000 was 
examined using aerial photography at four sites in 
Westernport Bay! The four sites were Rhyll 
(southern region), Corinella [eastern region], Stony 

It is difficult to estimate the exact seagrass area 
as published information is from overlapping zones and 
information is being constantly updated as mapping 
improves. The most accurate estimates of seagrass 
meadows along the northeast coast are 5668 km’? 
intertidal and shallow subtidal (down to 15 m water 
depth)": 39-50) 

From Cape York to Cairns, seagrass communities 
are predominantly subtidal Halophila species with 
approximately equal area of sparse and dense cover. 
Species of Cymodocea and Syringodium are found in 
shallow subtidal areas where there is shelter from the 
southeast winds. Between Cairns and Bowen, around 
70 percent of the area of seagrass is less than 10 
percent cover and mostly a mixture of Halodule and 
Halophila species, both intertidal and subtidal. 
Between Bowen and Yeppoon approximately 50 percent 
of the area of the mainly intertidal Halodule 
communities is between 10 and 50 percent cover. South 
of Yeppoon, the seagrass communities are mostly 

Point [eastern region] and Point Leo {southwest 
region). From 1956 to 1974, there was a decrease in 
seagrass distribution at three [Rhyll, Corinella and 
Stony Point) of the four sites. From 1973-74 to 1983- 
84 an 85 percent reduction of seagrass and 
macroalgal biomass, from 251 km? to 72 km’, was 
reported in the bay”””!, much of it on intertidal 
banks. A number of studies examined the causes of 
this dramatic loss of seagrass habitat”””*”” focusing 
on the effects of light reduction on seagrass 
communities as a result of increased sediment 
loads in the water column. These studies also 
examined the increased elevation of intertidal banks, 
the loss of pooling and the increased exposure of 
seagrasses to desiccation, a consequence of 
increased sediment inputs from catchment sources 
and resuspension of sediments in the water column. 
Annual sediment inputs from the northeastern 
catchment [>86 200 m‘/year) were found to be six to 
seven times the loads of sediments into other 
regions of the bay (13000 m’/year|" leading to 
decline in light availability in this region. Other 
causes such as the effects of industrial effluents on 
invertebrate fauna and subsequent reduced grazing 
of epiphyte loads were examined. No conclusive 
evidence was found that identified a single major 
factor as the cause of seagrass loss. The effects of 
seagrass loss on fish populations were also studied 
and findings suggested that Westernport Bay 
seagrass meadows play an important role in 
enhancing fish production and marine invertebrate 

denser, with approximately 60 percent of the area of 
seagrass greater than 50 percent cover. These 
seagrass areas are dominated intertidally by 
Zostera/Halodule communities and subtidally by 
Halophila communities. 

Waters of the Great Barrier Reef World Heritage 
Area deeper than 15 m have been surveyed and it is 
likely that as much as 40000 km’ of habitat that may 
support seagrass populations is present in the reef 
lagoon". The map in this case was based on spatial 
probability and cannot be compared with a map drawn 
from global position system points taken on the edge of 
a meadow. 

New South Wales, Victoria and Tasmania 

Estimates of seagrass area in New South Wales from 
mapping exercises prior to 1985 were 155 km’ in 111 
estuaries. In New South Wales the Conservation 
Division of New South Wales Fisheries is presently 
mapping seagrasses in large estuaries of the 

Subsequent mapping of seagrass and 
macroalgal habitats in Westernport Bay in 1995 
showed that seagrass and macroalgal cover in the 
bay had partly recovered, from an area of 72 km? in 
1983-84 to 113 km? in 1995. A further increase to 154 
km? was recorded in 1999" Despite these 
increases, the seagrasses in the north and 
northeast regions of Westernport Bay either remain 
in poor condition or have not recovered”. This is 
likely to be a result of poor water quality as 
chlorophylla and suspended sediment concen- 
trations increased in the northeastern waters of 
Westernport Bay between 1975 and 2000. This 
trend has reduced light availability and reduced the 
biomass and productivity of seagrasses. 

In April 2000, the effects of poor catchment 
practices and water quality again resulted in 
hundreds of hectares of seagrasses being lost during 
a flood event. Although some recovery of seagrasses 
has occurred over the last 15 years, seagrass 
meadows in Westernport Bay would still appear to be 
threatened by flooding and high turbidity even over 
time periods as short as days to weeks. 

The range of information from published 
papers and technical reports on Westernport Bay 
fails conclusively to attribute a single cause to the 
dramatic loss of seagrass from 1974 to 1984. By 
1999, seagrasses in the region had shown some 
recovery, more than doubling the area present in 
1984. Nevertheless, there are vast regions in West- 
ernport Bay that have failed to recover, or they are at 
their threshold of survival during high turbidity?” 

Eastern Australia 

Hawkesbury region and Port Hacking, but this 
information is not yet available. 

The Victorian Department of Natural Resources 
and Environment has recently produced maps for bays 
and inlets of Victoria that include 470 km’ of seagrass. 
Fine-scale maps (1:10000) detailing seagrass species 
composition and estimates of abundance have been 
produced for large bays including Gippsland Lakes, 
Corner and Nooramunga Inlets, Westernport Bay and 
Port Phillip Bay. Smaller inlets that have been mapped 
include Anderson, Mallacoota, Shallow, Sydenham, 
Tamboon and Wingham Inlets. The dominant seagrass 
communities include sparse to dense meadows of 
Zostera tasmanica, Zostera capricorni and Posidonia 

The Tasmanian Aquaculture and Fisheries 
Institute mapped areas of seagrass in six bioregions of 
Tasmania. The total area of mapped seagrass was 845 
km’. The Boags, Flinders and Freycinet bioregions have 
been mapped primarily from aerial photographs and 

These regions are closest to inputs of nutrients and 
sediments from a rapidly expanding urbanized 
catchment with extensive agricultural activities. 
Management strategies are being implemented to 
improve water quality in the northeast region by 
reducing flows of freshwater and loads of nutrients 
and sediments. These strategies are useful, but 
existing sediment resuspension issues and changes 
to intertidal bank topography will limit the possibility 
of full recovery of seagrass in this region. 




LANDSAT (1:100000 or greater). The Bruny bioregion 
has been recently mapped in detail from aerial 
photography with extensive ground-truthing’ *”. No 
mapping has been conducted in the Davey, Franklin and 
Otway bioregions, but it is unlikely there is much 
seagrass in these because of exposure to ocean swells 
and because of high tannin loadings in estuaries (i.e. 
Port Davey and Macquarie Harbour)". 

South gulf coast of South Australia 

Seagrasses in South Australia cover an area of 
approximately 9620 km’. Shepherd and Robertson” 
recognize three seagrass zones: exposed coasts, gulfs 
and bays, and coastal lagoons, each with different 
species composition. The exposed coasts are mainly 
patchy Posidonia typically where islands or reefs give 
local protection. The two gulfs which are a main feature 

Case Study 11.3 

Seagrasses are an integral and important part of 
coral reef systems. The Green Island seagrass 
meadows are one of many seagrass meadows found 
on reef platforms in the Great Barrier Reef waters'”! 
At a time when declines in seagrass biomass and 
distribution have been widely reported, Green Island 
is one of the few localities in the eastern Australian 
region where expansion of seagrasses has been 

Green Island is a vegetated coral cay located 
approximately 27 km northeast of Cairns. Ground- 
truthing and mapping of seagrass distribution was 
conducted in 1992, 1993 and 1994. Systematic 
mapping by transects was adopted on each occasion 
and vertical aerial photography (1:12000) was used if 
captured within the same season that ground 
surveys were conducted. Transects were located 
along compass bearings from permanent markers. 
A theodolite was used to accurately determine 
geographic location of survey sites [+1.5 ml. 
Estimates of above-ground seagrass biomass (three 
replicates of a 0.25 m? quadrat), species composition 
and sediment depth were collected every 20 m. 
Underwater video and still photography were used to 
provide permanent records. All data were entered 
onto a geographic information system. Boundaries 
of seagrass meadows were determined based on 
the geographic position of a ground-truthed site and 
aerial photograph interpretation. Digitally scanned 
and rectified vertical aerial photographs were used 
to map the past (1936, 1959 and 1972] seagrass 
distribution to the northwest of Green Island Cay. 

of the coast have a species gradient from entrance to 
head with Posidonia species being replaced with 
Amphibolis along the gradient. Three genera, Zostera, 
Ruppia and Lepilaena, are also found where intertidal 
mud flats occur. Coastal lagoons with a marine 
environment, such as the Coorong which is 100 km long 
and less than 2 m deep, are unique in this region. They 
feature an association of marine and brackish water 
genera such as Ruppia, Zostera and Lepilaena together 
with some marine algae’. 


Seagrass habitats in this region are noted for their 
importance as nursery areas for juvenile fish and for 
the commercial penaeid shrimp fishery in 
northeastern Australia. Coles et al.” recorded 134 
taxa of fish and 20 shrimp species in the seagrasses 


From the interpretation of aerial photographs, 
a high-density seagrass meadow of 0.39 +0.3 ha was 
first visible in 1936 as an isolated patch near the 
northwest tip of the cay. It appears to have expanded 
into the back-reef area northwest of Green Island in 
the 1950s to a small patch covering approximately 
1.1 +0.3 ha in 1959. It increased from the 1950s to 6.5 
+1.3 ha in 1972, 15.31 +2.29 ha in 1992, 22.71 +3.3 ha 
in 1993 and 22.9 +2.4 ha in 1994. A survey in 1997 
found little change”. 

In 1994 Halodule uninervis {average above- 
ground biomass, all sites pooled, 16.61 +1.4 g dry 
weight/m’) was the dominant species in the meadow. 
Cymodocea rotundata was the next most common 
species (3.95 +1.6 g dry weight/m’), with Cymodocea 
serrulata and Syringodium isoetifolium occurring in 
small patches of the meadow (4.12 +0.7 g dry 
weight/m’). Halophila ovalis (0.91 +0.3 g dry weight/ 
m*) occurred intermixed with Halodule uninervis 
beyond the intertidal and subtidal edges of the main 
meadow. Thalassia hemprichii was uncommon in the 
meadow (0.03 +0.02 g dry weight/m’). 

It has long been believed that the expansion of 
Green Island seagrass meadows was the result of 
biological and anthropogenic disturbances on the 
reef. It was first thought that the increases in area of 
the dense seagrass meadows to the northwest of 
Green Island Cay were linked to increases in tourist 
visitation and increased nutrients from the adjacent 
sewage outfall. This is because low nutrient 
availability dominates reef habitats such as Green 
Island and seagrasses are nitrogen limited". 

of Cairns Harbour. Seagrasses also provide food for 
dugong and green sea turtle which are the subject of 
conservation measures. 

Apart from licensed worm and bait collecting 
there is little or no gleaning activity on seagrasses in 
eastern Australia. 

Larkum et al.’ sum up the values of seagrass in 
six basic axioms: 
stability of structure; 
provision of food and shelter for many organisms; 
high productivity; 
recycling of nutrients; 
stabilizing effect on shorelines; 
provision of a nursery ground for fish. 

(sy (6) (S) fe} (©) e) 

In our view this remains an excellent summary of 
the uses and values of seagrass. 

In 1972, a sewage system for hotel buildings 
and public toilets on Green Island was established” 
Sewerage effluent from this was discharged onto 
the Green Island reef for 20 years, until December 
1992 when a tertiary treatment facility was 
completed. It is estimated that approximately 70-100 
m* of sewage was discharged per day". With no 
treatment to the effluent, it was essentially raw 
sewage (nutrient loads unknown] being dumped 
onto the western edge of the reef platform. 

It was, however, unlikely that sewage provided 
the major nitrogen source, as in September 1994, 
Udy et al") measured leaf tissue '"°N and recorded 
values from 1.3 to 1.7 parts per thousand suggesting 
that the primary nitrogen source comes from either 
fertilizers or No fixation®™. If the primary nitrogen 
source was from sewage, the seagrass would have 
had a leaf tissue 'N value closer to 10 parts per 
thousand. It could be assumed that '"N values 
would have been higher prior to the cessation of raw 
sewage discharge in 1992, but '°N values tend to be 
highly conservative due to internal recycling of 
nitrogen in the seagrass. 

Also, the expansion of the seagrass meadow 
before the sewage pipe was installed indicates that 
increased nutrient availability associated with the 
sewage outfall in 1972 was not a primary cause of 
the meadow expansion. This suggests other factors 
including water seepage and nutrient translocation 
from the cay, as well as regional changes 
(agriculture and urban development) in nutrient 
availability in Great Barrier Reef water may have 
caused the observed expansion prior to 1972. The 
continued expansion of the seagrass meadow after 
1972 may have been influenced by the sewage 

Eastern Australia 


Most Australian recorded losses of seagrass are 
probably the result of light reduction due to sediment 
loads in the water'“'. Quantifying loss of seagrass has 
been difficult in many locations as maps are often 
imprecise or unreliable and local change may be 
indistinguishable from map error’. Long-term data 
sets are not common so the extent to which loss of 
seagrass can be attributed to natural long-term 
cycles is impossible to estimate. Improved mapping of 
seagrass meadows will enable losses to be more 
accurately measured and tracked. 

Coastal development, dredging and marina 
developments are generic threats to seagrass in the 
tourist regions of Australia’s east coast. While these 
issues raise considerable public interest and concern 
they are usually closely managed through legislative 

discharge in addition to regional changes in nutrient 

Seagrass composition at Green Island con- 
tinues to change, with a rapid increase in the area of 
Syringodium isoetifolium which was first recorded at 
the island in the mid-1980s. With detailed maps and 
geographic information system (GIS) formats, 
changes in the future can be readily quantified and 
the dynamics of reef island seagrass meadows 
better understood. 


Source: Udy et al 

and Queensland Department of Primary 

ia yyy 
: Zo Breen sland 




1936 ER 1959 




oles, DPI 

Photo: R. { 


Thalassia hemprichii meadow on flat adjacent to Rhizophora forest, 
Piper Reef, Queensland 

processes and the actual areas of seagrass destroyed 
are generally small. 

Coastal agriculture may add to sediment loads in 
catchments and the presence of herbicides in seagrass 
sediments’ is a worrying trend, as unlike small-scale 
coastal developments, this has the potential to destroy 
large areas. Often the risk factors for the seagrass 
environment are many kilometers away in upper water- 
sheds. The Coorong Lakes seagrasses are affected by 
changes in nutrients and freshwater flows in the Murray 
River catchment which extends from South Australia up 
to central Queensland thousands of kilometers north. 

Port development and the management of risk 
can influence seagrass survival and many sheltered 
seagrass sites are also important port locations. The 
configuration of shipping lanes in northeastern 
Australia directs large ships transiting south of Papua 
New Guinea into Great Barrier Reef Lagoon waters. 
Shipping accidents remain a major concern for coastal 
habitats and, while infrequent, can be potentially 
devastating. Major programs exist in the western Pacific 
to provide advice on shipping-related incidents'*". 

Estuarine seagrass communities are increasingly 
the most threatened of the seagrass habitats in eastern 
Australia *’. As provincial centers develop along the 
Queensland coast, rivers and inlets are often highly 
affected and need careful management to maintain 
these seagrass habitats and the fisheries they support’”. 

Coastal habitats are threatened by coastal 
development as well as the impacts of runoff from 
poorly managed catchments, particularly when 
associated with large bays such as Botany Bay, 
Moreton Bay and Hervey Bay. 

Reef seagrass habitats are the least threatened 
seagrass community with minor damage from boating 
and shipping activities. High tourist visitation rates and 
associated sewage and poor anchoring practices are 
identified as a threat at some localities. Acute impacts 
such as ship groundings and associated spills would 
impact heavily on reef platform seagrasses. 

Although deepwater seagrasses are the least 
understood seagrass community, they could be 
impacted by coastal runoff (and associated light 
reduction] and to some extent prawn/shrimp trawling 
activities” “’, although the scale of any impact is largely 
unknown and difficult to determine. 


Seagrasses are habitat for juvenile fish and 
crustaceans that in many parts of the world form the 
basis of economically valuable subsistence and/or 
commercial fisheries. The need to manage fisheries in 
a sustainable way has itself become a motivating factor 
for the protection of seagrasses’. 

Approaches to coastal management decision- 
making are complex, and much of the information 
exists only in policy and legal documents that are not 
readily available. Local or regional government author- 
ities have control over small jurisdictions with 
regulations and policies that may apply. 

Approaches in eastern Australia to protecting 
seagrass tend to be location specific or at least state 
specific. The approach used depends to a large extent 
on the tools available in law and to the cultural approach 
of the community; in Australia these tools and 
approaches have their origin in British common law. 

While there is no international legislation, there is 
a global acceptance through international conventions 
(e.g. the Ramsar Convention on Wetlands, the 
Convention on Conservation of Migratory Species of 
Wild Animals and the Convention on Biological 
Diversity) of the need for a set of standardized data on 
the location and values of seagrasses. Numerous 
studies worldwide have presented ideas for seagrass 
protection. Cappo et al.'' summarized the main 
pressures on fish habitats and seagrasses in Australia. 
Leadbitter et al.’, Lee Long et al." and Coles and 
Fortes’ expanded the implications for research and 
management, a discussion that has Australian as well 
as global relevance. 

Protection by legislation 
In the eastern Australian states of New South Wales 
and Queensland, marine plants cannot be damaged 
without a permit” *. In Queensland, the legislation 
directly protects marine plants. Marine plants are 
defined as “a plant [a tidal plant] that usually grows on, 
or adjacent to, tidal land, whether living, dead, 
standing, or fallen”, a definition which includes living 
plants as well as seagrass plant material washed up on 
the beach. This definition recognizes the role of even 
dead plant material in the bacterial cycle that 
ultimately supports fisheries productivity. 

The Queensland Fisheries Act allows for 
destruction or damage of seagrass only when a permit 

has been assessed and issued. All permit issue is 
directed by a policy that must be taken into account by 
the person delegated under the Act to make the 
decision. The policy requires that no reasonable 
alternative exists. In states such as Queensland, fines 
well in excess of US$0.5 million are applicable for 
damaging seagrasses, with the possibility of associated 
restoration orders. 

All eastern Australian states have similar 
protections in either Fisheries Acts or in National Park 
or Marine Park Acts. Australia, in fact, has approxi- 
mately 40 legislative instruments that directly influence 
marine plant and/or seagrass management’, not 
including regulations and management plans that as 
subsidiary legislation may also be operationally vital to 
seagrass protection. An example of this would be 
fisheries legislation that limits areas where bottom 
trawling can take place. 

Protection by marine protected areas (MPAs) 
Overlying state and local approaches, Australia also 
has national legislation addressing international issues 
such as treaties and conventions including the 
Convention on International Trade in Endangered 
Species of Wild Fauna and Flora (CITES) and world 
heritage area declarations. The Great Barrier Reef 
World Heritage Area is protected in legislation by the 
world’s largest MPA, the Great Barrier Reef Marine 
Park. This is unique in that it possibly has as much as 
40000 km’ of seagrass”, much of which is afforded a 
level of protection by the MPA. This can lead to 
confusingly high levels of regulation; a seagrass 
scientist working in east coast tropical Queensland 
requires permits and must meet conditions from 
national and state authorities. 

However, the Great Barrier Reef Marine Park 
model would not be appropriate in many situations as 
the money to fund a large administrative authority, 
legislative support, ongoing research and long-term 
monitoring, and compliance is not available. More 


1 Walker DI, Dennison WC, Edgar G [1999]. Status of Australian 
seagrass research and knowledge. In: Butler A, Jernakoff P [eds] 
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D Plan. CSIRO, Collingwood. pp 1-24. 

2 Lee Long WJ, Mellors JE, Coles RG [1993]. Seagrasses between 
Cape York and Hervey Bay, Queensland, Australia. Australian 
Journal of Marine and Freshwater Research 44: 19-31. 

3 Coles RG, Lee Long WJ, McKenzie LJ, Roelofs AJ, De’ath G [2000]. 
Stratification of seagrasses in the Great Barrier Reef World 
Heritage Area, Northeastern Australia, and the implications for 
management. Biologia Marina Mediterranea 7(2]: 345-348. 

4 Coles RG, Poiner IR, Kirkman H [1989]. Regional studies - 
seagrasses of North-eastern Australia. In: Larkum AWD, McComb 
AJ, Shepherd SA (eds) Biology of Seagrasses: A Treatise on the 
Biology of Seagrasses with Special Reference to the Australian 
Region. Elsevier, Amsterdam. pp 261-278. 

Eastern Australia 

common are MPAs specific to a site and designed to 

protect an area identified as having important 

ecosystem functions. 

The Queensland Fisheries Act‘ allows for the 
establishment of fish habitat areas (FHAs) that include 
areas of coastal seagrass. FHAs are usually small (up to 
several thousand hectares) MPAs designated specifically 
to protect fisheries habitat structure over areas 
considered especially important or critical to fisheries”. 

In recent years there has been a growing 
realization that we should identify and protect 
representative examples of the diversity of habitats and 
processes upon which species depend rather than just 
areas identified as having some especially important 
characteristic’. A representative area is an area that is 
typical of the surrounding habitats or ecosystem at a 
chosen scale. This approach would: 
fo) maintain biological diversity at the ecosystem, 

habitat, species, population and genetic levels; 

allow species to evolve and function undisturbed; 
provide an ecological safety margin against 
human-induced and natural disasters; 

) provide a solid ecological base from which 
threatened species or habitats can recover or 
repair themselves; 

() maintain ecological processes or systems. 

Typical of establishing a representative area 
approach to protecting seagrasses is the need for very 
detailed maps and quantitative data on species and 
biomass. Presently this information is inadequate for 
many of our seagrass areas. Compiling a global report 
card and synthesis of seagrass knowledge will provide a 
base for future protective decisions and implementation. 


Rob Coles, Len McKenzie and Stuart Campbell, Queensland Department 
of Primary Industries, Northern Fisheries Centre, P.O. Box 5396, 
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the interaction between physiology, morphology and stable isotope 
ratios in five species of seagrass. Journal of Experimental Marine 
Biology and Ecology 195: 91-110. 


12 The seagrasses of 


ew Zealand (Aotearoa) is an isolated archi- 
N pelago, consisting of two main islands and a 

number of smaller islands which lie in the 
southern Pacific Ocean. Until quite recently, the 
seagrass flora of New Zealand was thought to consist 
of two species of Zostera: Zostera capricorni, which 
also occurs in eastern Australia, and an endemic 
species, Zostera novazelandica. {Two species of Ruppia 
- Ruppia polycarpa and Ruppia megacarpa - also occur 
in brackish and freshwater wetlands in New Zealand", 
but are not considered further here.) Zostera 
novazelandica was originally described by Setchell in 
1933 on the basis of morphological variation in 
vegetative characters, using a relatively limited sample 
of plants”. In fact, there is quite large morphological 
variation within natural stands of Zostera in New 
Zealand and reproductive structures occur infrequently 
in many populations’®. This variation has caused 
considerable uncertainty in identification over the past 
century, and workers have variously referred to the 
New Zealand Zostera as Zostera nana, Zostera 
muelleri, Zostera marina and Zostera tasmanica“”"'. A 
recent molecular phylogeny of the Zostera group, 
however, demonstrated that Zostera capricorni and 
Zostera novazelandica are, in fact, conspecific and that 
there is likely to be only a single species in New 
Zealand, hereafter referred to as Zostera capricorni”. 


Zostera capricorni occurs throughout the mainland 
coast of New Zealand, from Parengarenga Harbour in 
the north to Stewart Island in the south (Tables 12.1 and 
12.2). It is found predominantly between mid and low 
tidal levels in estuaries and sheltered harbors". On the 
eastern coastline of the two main islands, patchy 
stands of Zostera capricorni also occur on the tops of 
siltstone platform reefs in open coastal areas, where 
they are interspersed with algal beds and biotic 
assemblages more characteristic of rocky, intertidal 

G.J. Inglis 

assemblages” |". Stands vary in extent, biomass and 
stability, depending upon their location” * '”. In large, 
shallow estuaries subject to wind fetch, and on 
platform reefs exposed to oceanic waves, stands of 
Zostera capricorni typically consist of a mosaic of 
patches that range in size from less than 1 m’ to 15 m* 
and which exhibit large interannual fluctuations in 
extent '* "|. The largest persistent stands appear to 
occur in estuaries and embayments with relatively 
clear, tidal waters that are situated away from major 
urban centers, such as Parengarenga Harbour, 
Farewell Spit, Whanganui Inlet and estuaries of the 
eastern Coromandel Peninsula. 

Despite the wide geographic distribution of 
Zostera capricorni in New Zealand, there have been 
relatively few published studies of its extent, 
demography or ecology. Part of the reason for this may 
be its relative scarcity in many New Zealand estuaries. 
Zostera capricorni is absent from, or occurs in 
relatively small areas within, many of the shallow, 
turbid estuaries in New Zealand. Seagrass habitats 
have been mapped in only 22 of New Zealand's 300- 
plus estuaries (Table 12.1). The areas that have been 
mapped typically represent less than 3 percent of the 
total intertidal area of each estuary. Exceptions include 
tidally dominated embayments, such as Whanganui 
Inlet and Whangamata, where seagrass meadows 
cover up to 31 percent and 18 percent of the intertidal 
area, respectively. Just over half (54 percent] of New 
Zealand's estuaries are unsuitable for seagrass growth 
as they are shallow, barrier-formed estuaries, built 
around the mouths of rivers'“', so Zostera capricorni is 
likely to be a relatively uncommon benthic habitat in 
many estuarine environments. 


Zostera capricorni stands in New Zealand, like those 
elsewhere in the world, support a diverse and abundant 
assemblage of invertebrates that is often richer than 

unvegetated habitats nearby” ' 7". The composition 

of the invertebrate assemblages varies with the size 
and stability of the seagrass stand and its position 
relative to other habitats’. Bullomorph and proso- 
branch gastropods are distinctive components of the 
epibenthic fauna’. Small crustaceans and polychaetes, 
which are particularly abundant within seagrass 
meadows, are important sources of food for wading 
birds, such as the South Island pied oystercatcher, bar- 
tailed godwit, pied stilt and royal spoonbill; and for 
fishes such as mullet, stargazers and juvenile 
flatfish®. Seagrass fragments are also a common 
food of garfish (family Hemirhamphidae], which are 
popular with recreational fishermen”. 

Large densities of small cockles, Austrovenus 
stutchburyi, and other bivalves are common in 
seagrass habitats” *”*'. Many of these species are not 
restricted exclusively to seagrasses, but are often 
more abundant within them as juveniles. Several 
authors have also drawn a_ strong historical 
association between the distribution of seagrasses 
and beds of the New Zealand scallop, Pecten 
novazelandiae™ *". However, the life cycle of the Pecten 
novazelandiae is not dependent on seagrass habitats 
and commercial stocks exist in areas where Zostera 
capricorni is not present’. 

A recent survey of more than 25 harbors in 
northern New Zealand suggests that seagrasses may 
be important nursery habitats for newly settled 
snapper (Pagrus auratus, family Sparidae]”. Snapper 
is arguably New Zealand’s most sought-after marine 
fish and is the subject of a large commercial and 
recreational fishery. Adult snapper spawn in large bays, 
but juveniles are found predominantly in sheltered bays 
and shallow estuaries during their first summer, before 
they move to deeper coastal waters’. Snapper under 
one year old have been found in few other coastal 
habitats and appear to occur mostly in clear-water, 
sandy reaches of estuaries, the areas most favorable to 
seagrass growth. Juveniles of other estuarine and 
coastal fishes are also abundant in seagrass 

The presence of Zostera capricorni on siltstone 
platform reefs allows some estuarine species to inhabit 
these open coastal environments. For example, the 
endemic burrowing crab Macrophthalamus hirtipes 
occurs exclusively in Zostera capricorni on siltstone 
reefs, where it feeds on seagrass detritus and 
associated invertebrates”. On estuarine mud flats, 
Macrophthalamus hirtipes is more widespread and not 
necessarily restricted to seagrasses. 

The lack of detailed mapping and long-term study of 
seagrass habitats in New Zealand makes it difficult to 

New Zealand 

+ Parengarenga Harbour 
Houhora Harbour "Ue NSarensa 1% 

Whangarei Harbour 

Kaipara Harbour Firth of Thames 

Auckland Coromandel Peninsula 

Manukau Harbour £ 
@ Whangamata 

«Tauranga Harbour 

HO? s Kawhia Harbour . 

Waimea Inlet North Island 
Farewell Spit 
Whanganui Inlet ¢ 

» Te Angiangi 
Marine Reserve 

Oharito Lagoon Pee or 

¢ Kaikoura Peninsula 
South Island Christchurch 
e » Purau Bay 
fkaroa Harbour 


Lagoon , 

Otago Harbour 

a. 0 100 200 300 Kilometers 
Stewart Island “Awarua Bay — 
165° E 170° E 

175° E 180° E 
Map 12.1 
New Zealand 

determine how their distribution and extent have 
changed over time. Seagrass meadows undoubtedly 
supported elements of the economies of pre-European 
and early European life in New Zealand. The name 
given to Zostera capricorni by New Zealand's 

Table 12.1 
Area of seagrass in New Zealand estuaries where benthic 
habitats have been mapped 

Estuary Total area of 
Zostera capricorni km’) 
Mahurangi Harbour''”! 0.03 
Whangateau Harbour!” 0.33 
Pahurehure Inlet (Manukau Harbour)!” 
Arm of Kaipara Harbour'”®! 
New River Estuary'"®! 
Matakana Harbour 
Manaia Estuary'””! 
Whitianga Harbour 
Tairua Harbour” 
Whangamata Estuary 
Wharekawa Estuary'*”” 
Otahu Estuary” 
Te Kouma Estuary 
Firth of Thames?” 
Tauranga Harbour” 
Ohiwa Estuary"®! 
Waimea Estuary 
Whanganui Inle 
Avon-Heathcote Estuary 
Kaikorai Estuary!" 
Harwood, Otago Harbour 













indigenous Maori - rimurehia - suggests that they may 
have recognized the food value of its starchy 
underground rhizome. Rimu is the general term for 
seaweed or sea plant and réhia was a type of jelly-like 
stew that was made by boiling marine plants [more 
usually algae] with tutu berries, the fruit of a wetland 
plant (Coriaria spp.)'“'. Seagrass leaves were also 
occasionally used by Maori to adorn items of clothing. 
Hamilton in 1901 described widows wearing mourning 
caps (potae taual that had veils made from seagrass’. 

Historical accounts by early European naturalists 
suggest that meadows were quite widespread at the 
end of the 19th century. Colenso in 1869 described 
them as “very plentiful” and occurring in “many places 
in the colony” from the top of the North Island to 
Stewart Island’*°”. Leonard Cockayne (1855-1934) 

Table 12.2 

Location Description 

Parengarenga Harbour'"! 
and bird populations 

Muriwhenua Wetlands?" 

Whangarei Harbour’ *"! 


described Zostera as “extremely common in shallow 
estuaries” where it “covers the muddy floor... for many 
square yards at a time”. At that time, seagrass was 
apparently so abundant that at least two authors 
proposed harvesting it for export to London, where 
dried Zostera fetched between £7 10s and €10 per ton 
as a stuffing for mattresses and upholstered 
furniture’ *’. This suggestion does not appear to have 
been acted upon. Other accounts describe Zostera as 
“common in many of the lagoons and estuaries which 
occur along the coast"”’, and as covering “extensive 
areas of sheltered mud flats between the tides””. 
Oliver in 1923 described extensive meadows of Zostera 
in Parengarenga Harbour, Tauranga Harbour and 
Golden Bay, Stewart Island”. According to him, 
"masses of Zostera” were occasionally torn up by 

List of locations where seagrasses have been recorded in New Zealand 

Extensive tidal sand flats (42 km’) mostly covered in seagrass. Important feeding grounds for large fish 

Includes Houhora (10.5 km’) and Rangaunu Harbours (74 km’). Extensive tidal sand flats mostly 
covered in dense beds of seagrass, supporting abundant mollusks, polychaetes, anemones, asteroids 
and crustaceans. Important feeding grounds for large fish and bird populations 

Lush seagrass beds present until late 1960s. Some recent recovery 

Whangapoua Wetlands 
Waitemata Harbour”! 
Tairua Estuary?” 
Whangamata Estuary 
Wharekawa Estuary” 
Kaipara Harbour"! 
Manukau Harbour 


(12, 13, 21) 

Firth of Thames") 
Kawhia Harbour?” 
Tauranga Harbour"! 
Maketu-Waihi Estuaries"! 
Ohiwa Harbour'"® 2°21) 

Ahuriri Estuary and Wetlands: 

Te Angiangi Marine Reserve-East’” 

Te Tapuwae 0 Rongokako 
Pauatahanui Inlet!**! 

Farewell Spit?" 

Seagrass present on mud flats (ca14% of the area]. Significant site for shellfish gathering 

Seagrass meadows much reduced since 1960s, now in small abundance in a range of locations 
Around 1.25 km? in 1995, covering ca 23% of the tidal flats 

Around 0.51 km’ in 1995, covering ca 18% of the tidal flats 

Around 0.50 km? in 1995, covering ca 32% of the tidal flats 

Extensive mud flats and sand flats, but limited area of seagrass 

Extensive intertidal mud flats with large beds of seagrass in the 1960s. Current stands are patchy and 
temporally variable 

Internationally important feeding area for waterfowl (Ramsar Site]. Around 0.3 km’ of seagrass on 

tidal flats of ca 85 km* Traditional food gathering area. Important local fisheries for snapper and flounder 
Seagrass beds often present on tidal sand and mud flats 

Around 29.3 km? of seagrass remaining (1996). Decline of 34% overall from 1959 and 90% in subtidal 
meadows. Important shellfishery, spawning and nursery areas for marine fishes 

Intertidal mud flats and sand flats have local areas of seagrass 

About 23.8 km’ of intertidal flats with 1.1 km? of seagrass. Outstanding 

importance as an area for traditional shellfish collection 

Patches of seagrass in the marine reaches of the estuary, along with 

Ruppia and green algae. Important nursery for fish. High diversity and abundance of invertebrates, 
especially cockles 

Patches of seagrass on coastal reefs. Marine reserve 

Patches of seagrass on coastal reefs. Marine reserve 

Large areas of Zostera capricorni on the banks of the inlet near deltas of Horokiwi and 

Pauatahanui streams 

Extensive areas of sand and mud flats. Large areas of seagrass. 

Internationally important area for waterfowl (Ramsar site] 

storms and washed onto beaches or swept out to sea in 
these areas. 

In the major South Island city, Christchurch, mud 
flats of the Avon-Heathcote Estuary were reportedly 
“covered in great expanses of eelgrass (Zostera]” prior 
to European settlement". Early photographs clearly 
show dense meadows lining the sand banks of the main 
channels“ and accounts described seeing eels 
feeding in “lush paddocks” of seagrass that grew in the 
deep channels“). Later records document the rapid 
disappearance and stuttering recovery of Zostera in the 
estuary. By 1929, the “lush paddocks” had been 
reduced to sparse, small patches’. Loss of the 
meadows was associated with the decline of small 
fisheries for shrimp and periwinkles in the estuary and 
caused a “severe and rapid degradation” of feeding 

New Zealand 

grounds for wading birds, which were hunted 
extensively at the time for food and sport” “". At least 
ten families had made their living harvesting shrimp 
from what they referred to as “shrimp grass"“”. By 
1952, the seagrass had disappeared almost completely, 
with only a few, very small patches remaining in the 
northern channel of the Avon River'!. Since then, 
patches have waxed and waned in abundance. By 1970 
Zostera had almost completely disappeared'’*“”. In 
1981, small patches covered around 14 percent of the 
tidal flats, but these disappeared later in the same year 
with almost complete defoliation occurring in many 
areas”. The most recent surveys, in 1999, show a total 
area of around 0.137 km’ that comprises around eight 
consolidated patches'"”’. 

Seagrass losses have also been reported in other 


Whanganui Inlet": 7! 

Waimea Inlet!" 2” 
Parapara Inle 
Moutere Inlet'®?! 


Waikawa Bay (Queen Charlotte]'**’ 
Wairau Lagoons" *! 

Kaikoura Peninsula’ ° * 
Karamea Estuary’? 
Saltwater Lagoon 
Okarito Lagoon": °*! 


Avon-Heathcote Estuary, 
Christchurch'2": 4” 

Akaroa Harbour'®”! 

Purau Bay, Lyttleton Harbour” 

Brooklands Lagoon'“* **! 

Otago Harbour!” *”! 

New River Estuary 

Awarua Bay'"! 

Toetoes Harbour 



Paterson Inlet, Stewart Island!” 
Moeraki Beach'*”! 

Mahurangi Harbour 
Whangateau Harbour 
Whitianga Harbour” 
Manaia Harbour”! 
Te Kouma Harbour 
Otahu Estuary”! 





Large seagrass beds (8.6 km’], especially in the northern part of the inlet. 

Important nursery for marine fishes. Marine reserve 

Extensive bar-built estuary. Around. 0.28 km’ of seagrass 

Zostera capricorni on silt deposits on the rock platform and on mud flats 

Large mud flats with extensive beds of Zostera capricorni and shellfish. 

Important nursery for marine and freshwater fishes 

Patches of Zostera capricorni present 

Extensive areas of algae, Ruppia megacarpa and some Zostera. Nursery 

habitat for marine and freshwater fishes 

Zostera capricorni present on coastal siltstone reefs at Wairepo flats and Mudstone Bay 

Mud flats with extensive areas of seagrass and large densities of invertebrates 

Bare or sparsely vegetated tidal mud flats 

Middle reaches of lagoon dominated by Zostera, upper reaches characterized by dense beds 

of Ruppia, Lepidena and Nitella 

Patches of seagrass grow between low and mid tide close to the Avon Channel. Seagrass more 
abundant prior to 1929. Nationally important area for waterfowl. Among the most important food 
gathering sites for South Island Maori in pre-European times 

Extensive areas of seagrass on tidal flats at Duvaechelle and Takamatua Bays 

Patches of seagrass 

Scattered, large circular patches of Zostera capricorni prior to 1978. None recorded in 1991 
Around 0.8 km? of seagrass on tidal flats at Harwood 

Extensive mud flats with seagrass. Important source of kaimoana. Nationally important wildlife area 
Extensive mud flats with seagrass. Important source of kaimoana. Nationally important wildlife area 
Mud flats with extensive areas of seagrass and large densities of invertebrates. Nationally 
important wildlife area 

Mud flats beyond the river mouth support seagrass 

Patches of seagrass on coastal reefs 

Around 0.03 km? in 1999 in a single meadow. 

Around 0.33 km? in 1999 consisting of two main beds in the southern arm 
Around 0.5 km? in 1995, occupying ca 0.6% of the estuary area 

Around 0.27 km? in 1995, covering ca 7.5% of the estuarine flats 

Around 0.05 km? in 1995, covering ca 2% of the tidal flats 

Around 0.002 km? in 1995, covering ca 0.4% of the tidal flats 




parts of the country. Zostera was reputedly once very 
abundant in Waitemata Harbour, the location of New 
Zealand's largest city, Auckland (population ca 1 
million). Before 1921, seagrass dominated large areas 
of Hobson Bay and Stanley Bay, but by 1931, it had all 
but disappeared” *'. Powell" associated this loss with 
marked reductions in catches of snapper and other 
carnivorous fishes. At the time, he speculated that “in 
respect to depletion of harbour fishing grounds 
generally [loss of seagrass] may be a more important 
factor than either over-fishing or assumed harbour 
pollution”. This hypothesis has been given greater 
weight by research that suggests an important nursery 
role of seagrasses for juvenile snapper'”. 

Extensive meadows in the Tamaki Estuary, 
Howick Beach, Okahu Bay, Kawakawa Bay, Torpedo 
Bay and Cheltenham in the Auckland district that 
were present during the early 1960s disappeared by 
the 1980s""’. Well-developed stands of seagrass also 
occurred on Te Tau Banks and along the northern tidal 
flats of Manukau Harbour in the early 1960s!” 
Descriptions at the time referred to “splendid Zostera 
fields of the Manukau Harbour... in some places up to 
a mile across". Most of these areas had also 
disappeared or were severely reduced in size by the 
early 1980s”, 

Further north, “lush beds” of seagrass on mud 
flats in Whangarei Harbour disappeared in the early 
1960s'“*". In Tauranga Harbour, Park recorded a 
decline of around 15 km* (about a third of the total area 
of seagrass) between 1959 and 1996’. Subtidal 
meadows were most affected, with just 0.46 km? 
remaining out of the 4.79 km? present in 1959 (a 90 
percent reduction). 

The causes of these declines are generally 
unclear. They have variously been attributed to a range 
of different human activities and natural events. In the 
Avon-Heathcote Estuary, the loss was linked to the 
practice of “river sweeping” which began in 1925 to 
clear silt and plant growth that had accumulated in the 
two rivers which feed into the estuary’. Large 
quantities of sediment were released during the 25 
years that the sweeper operated, producing a muddy 
sediment layer in the estuary up to 25 cm deep. 
Untreated sewerage effluent and industrial waste from 
the rapidly growing city of Christchurch were also 
discharged into the estuary at this time and may have 
contributed to the decline“. In Waitemata Harbour, the 
disappearance of seagrass was attributed to waterfront 
construction, channelization of tidal streams and runoff 
of fine sediments from surrounding land develop- 
ment’. In Whangarei Harbour, a major cement works 
discharged around 106000 metric tons of limestone 
washings each year into the surrounding waters. The 
discharge significantly reduced water clarity and has 

been implicated in the disappearance of extensive areas 
of seagrass’ *"! 

Armiger reported the widespread die-back of 
seagrass throughout New Zealand during the 1960s'"". 
In 1964, she isolated a slime mold from some of the 
affected populations that resembled Labyrinthula 
zosterae”, the pathogen responsible for the infamous 
wasting disease epidemic in North Atlantic Zostera 
during the 1930s'**. Subsequent collections and 
observations showed that the mold and symptoms of 
die-off were present throughout both the North and 
South Islands*". Other studies have reported sporadic 
outbreaks in some populations’**“”. Curiously, the first 
recorded disappearance of seagrass meadows in New 
Zealand, from Waitemata Harbour and the Avon- 
Heathcote Estuary, occurred at much the same time as 
the northern hemisphere epidemic and corresponded 
with reports of the large-scale disappearance of 

Zostera in South Australia". 

There has been no recent assessment of the condition 
of New Zealand's estuaries and, therefore, of 
contemporary threats to seagrass habitats. New 
Zealand is relatively sparsely populated {ca 3.8 million 
people in a total land area of 268021 km‘) so that, 
although most of its estuaries have settlements 
nearby, only six are located within urban environments 
that contain more than 80000 people’. Estuarine 
habitats have, however, been progressively modified 
since the times of Polynesian {ca 800 years ago) and 
European [ca 200 years ago) settlement. Land 
clearance, shoreline reclamation, harbor development, 
flood mitigation works and discharge of pollutants have 
had direct impacts. Less than 23 percent of the land 
area of the country now remains in native forest with 
significant areas converted to agricultural production 
(51 percent] or plantation forestry (6 percent]! 
Sedimentation is the most widespread problem in 
New Zealand’s estuaries. New Zealand is a 
predominantly mountainous and hilly country, with 
nearly half of the land mass at slopes steeper than 28 
degrees. Its rivers carry a particularly high load of 
suspended sediments as a result of the steep terrain 
and relatively high annual rainfall"!. Deforestation and 
rural land management have exacerbated the delivery 
of suspended sediments to coastal areas and many of 
New Zealand's larger estuaries are very turbid (light 
attenuation coefficients up to 0.75/m’‘), with compara- 
tively high rates of sediment accretion. In some 
northern estuaries, this has meant that the area of 
intertidal habitat has slowly been reduced by increases 
in the area of mangroves and supratidal salt marsh. 
Losses of seagrass habitat have been attributed to 
increased sedimentation and turbidity in a number of 

estuaries'“*7“4°2° and it remains the biggest 

challenge for restoration of submerged aquatic 

Large areas of plantation forest are now coming 
into production in New Zealand and harvests are 
expected to double within the next ten years to more 
than 600 km’ per year. The largest increases are likely 
to occur in regional areas of the North Island 
(Northland, Coromandel, East Cape, Hawkes Bay, and 
southern North Island), and to include areas bordering 
some of the most significant remaining areas of sea- 
grass {e.g. Parengarenga, Houhora and Coromandel 
Harbours). It will be important for industry and regional 
authorities to manage sediment and nutrient runoff 
from this activity to avoid additional impacts on the 
ecology of these estuaries. 

Nutrient enrichment from land-based sources is a 
significant problem in some urban estuaries. Recurrent 
blooms of macroalgae in Tauranga Harbour and the 
Avon-Heathcote Estuary in Christchurch have been 
attributed to nutrient loads from wastewater discharge 
and urban runoff. No direct studies have been done of 
the effects of nutrient loading from these sources on 
seagrass growth, although both estuaries have had 
significant seagrass meadows in the past”*“““”". Less 
information is available on nutrient loads to estuaries 
outside the major urban centers. The most widespread 
sources of nitrates entering New Zealand rivers are 
likely to be associated with effluent and runoff from 
agricultural production’. It is unclear what impacts 
these diffuse sources have had on seagrass habitats. 

In some areas, recreational activities have had 
localized impacts on seagrasses”. In Otago Harbour, 

Figure 12.1 

New Zealand 

for example, horse riding and four-wheel drive bikes 
occasionally rip up rhizomes and roots leading to the 
formation of large bare patches that can take longer 
than one year to regrow. Heavy trampling (more than 
ten passes in one area) across the seagrass flats has 
also been shown to cause trench formation and lasting 
damage, but it is unclear how widespread this is”. 

Occasional, recurrent outbreaks of wasting 
disease appear likely in New Zealand seagrass 
populations. Further study is required to understand 
the epidemiology of these outbreaks and, in particular, 
if they are exacerbated by human activities. In the first 
instance, this requires an understanding of the 
resilience of different meadow types (e.g. large versus 
patchy, persistent versus ephemeral) to outbreaks of 
the disease and the method of transmission of the 
pathogen from one location to another. 

Nevertheless, there are positive signs that 
seagrass meadows are Slowly returning to some areas 
from which they had been lost. In Whangarei Harbour, 
improvements in water quality over the past two 
decades have led to the re-establishment of 
seagrasses in areas from which they had disappeared. 
Discharges of limestone washings into the harbor 
ceased in 1983 and, since then, improvements in 
sewerage wastewater and other discharges have 
greatly increased water quality’. This pattern has 
been repeated in other estuaries as point sources of 
pollution have been removed or have been better 
managed over the past 20-30 years. Regrowth of 
seagrasses in the Avon-Heathcote Estuary is no doubt 
attributable, in part, to improvements in water quality 
that have been made through upgrading treatment of 

An example of changes in the historical distribution of seagrasses in New Zealand 

Ref: 897 1/2 


P{hoto: G. Inglis 

Moncks Bay in the Avon-Heathcote Estuary, Christchurch at low tide in 1885 [left] and 2003 [right]. The channel morphology has changed 
considerably since 1885 and the once extensive intertidal sand banks have all but disappeared. Seagrass meadows, which can be seen 
clearly as dark bands lining the sand banks in 1889, are no longer present. It is unclear whether the change in channel morphology 
preceded the loss of seagrass or resulted from it, as the root and rhizomes of seagrass meadows trap and hold soft sediments in place. 




wastewater and urban runoff and ending disturbance of 
river habitat’“*”. Non-point sources of pollution and 
urban stormwater, however, remain significant 
problems for many estuaries. 


Seagrasses and other aquatic macrophytes are not 
specifically protected by legislation in New Zealand, but 
are provided for under a variety of resource man- 
agement and conservation legislation. Responsibility 
for the protection and management of coastal habitats 
is split among several national and regional 

The Resource Management Act 1991 [RMA] is an 
overarching piece of legislation that governs the use of 
most natural and physical resources [excluding 
fisheries) in New Zealand. Under the RMA, regional 
authorities have principal responsibility for managing 
the use of coastal environments and are required to 
prepare regional coastal plans as the strategic basis 
for guiding decisions about resource use in these 
areas. Development activities within the coastal 
marine area require approval (“resource consent") 
from the local authorities under the RMA and must be 
consistent with the provisions of the coastal plan. 
Priorities for coastal management were set by the 
Minister of Conservation in the New Zealand Coastal 
Policy Statement and these serve as a guide for 

Case Study 12.1 

An unusual seagrass specialist in New Zealand Is 
the small endemic limpet, Notoacmea helmsi 
(scapha] (see drawing, right). This species appears 
to occupy an almost identical niche to the North 
Atlantic species Lottia alveus, which reputedly 
became extinct during the wasting disease epidemic 
of the 1930s? Like Lottia alveus, Notoacmea 
helmsi(scapha) is a small, elongate limpet (ca 4 mm 
long x 1.75 mm wide) that fits perfectly onto the 
narrow leaves of Zostera”. 

Unfortunately, there have been no studies of 
its life history, so it is unclear if it is as specialized as 
its North American counterpart and, although it was 
reportedly once widespread in New Zealand, there 
is no contemporary information on its distribution 
and abundance. The absence of detailed study also 
means that there is some uncertainty about whether 
Notoacmea helmsi {scapha) is a true species or 
simply a morphological variant of the larger 
estuarine limpet Notoacmea helmsi helmsi**. 

The New Zealand limpet provides a unique 

development of the regional coastal plans. Wetlands 
are specifically identified as a “matter of national 
importance” in the RMA that must be taken into 
account when decisions are being made about 
resource use. Because of this, many freshwater and 
estuarine wetlands are specifically listed as “areas of 
significant conservation value” in existing and 
proposed coastal plans, and are subject to relatively 
strict development controls. In some instances, 
regional authorities have used regulatory measures 
such as estuarine protection zones to exclude 
damaging activities from sensitive environments. 
Regional authorities are also responsible for 
maintaining coastal water quality under the RMA and 
regulate land-based activities that can detrimentally 
affect water quality. 

The New Zealand Fisheries Act 1996 provides for 
the “utilization of fisheries resources while ensuring 
sustainability”. This includes managing the current and 
potential production of fisheries in New Zealand and 
their impact on the habitats that support them. 
Although marine vegetation is not specifically mention- 
ed in the Act, it establishes environmental principles to 
guide the utilization of fisheries resources. These 
include the “maintenance of biological diversity” and 
the "protection of habitat of particular significance for 
fisheries management”. Provisions allow for the pro- 
tection of specific areas that are important for local and 

opportunity to study the causes of rarity and 
extinction in marine environments and to determine 
what impact [if any) loss of the North Atlantic limpet 
may have had on other species that live and feed in 
seagrass meadows. 

Morphology and habit of the New Zealand seagrass limpet 
Notoacmea helmsi(scapha). 

Source: Redrawn from Morton and Miller) 

customary fisheries (ta/apure}, traditional fishing 
(mataitai) and for the protection of specific stocks or 
their habitat. 

Legal protection of coastal waters is mostly 
administered by the Department of Conservation under 
the Marine Reserves Act 1971. Marine reserves contain 
the highest level of protection for natural marine 
environments in New Zealand; all species and habitats 
are protected from exploitation. There are currently 16 
marine reserves in New Zealand that encompass 
around 7633.5 km?. However, only two of these contain 
significant areas of seagrass. Whanganui {Westhaven] 
Inlet contains around 8.59 km? of seagrass”! which are 
protected through a combination of a marine reserve 
and a wildlife management reserve that cover a total 
area of 26.48 km’. Te Angiangi Marine Reserve, on the 
east coast of the North Island, also encompasses 
extensive stands of seagrass on intertidal platform 
reefs'''. The exact area of seagrass in the reserve is not 
known, but in this open coast environment it is likely to 
be highly variable”. 

The Wildlife Act 1953 and Reserves Act 1977, also 
administered by the Department of Conservation, have 
been used to protect intertidal habitats in some 
estuaries where there are important wildlife, scenic, 
scientific, recreational or natural values. 

Five wetlands in New Zealand are registered 
under the Ramsar Convention as of special importance 
to wading birds”". Three of these contain coastal or 
marine environments that include areas of seagrass. 
Farewell Spit, on the northwest of the South Island, 
contains an extensive area of intertidal sand and mud 
flats with Zostera capricorni meadows". It has been 
protected as a Nature Reserve since 1938 and is a 
significant area for a variety of wading birds and 
waterfowl. In particular, it is the site of the major 
molting congregation of the native black swan, Cygnus 
atratus. More than 13000 swans have been recorded in 
the area, at densities of up to 1000 birds per km’. 
During these congregations, Zostera capricorni is the 
largest component of their diet. The two other coastal 
Ramsar sites are in the Firth of Thames in the North 
Island and Waituna Lagoon at the southern tip of the 
South Island. 


The collage of historical and contemporary information 
assembled in this review suggests strongly that 
seagrass habitats were once much more widespread in 
New Zealand's estuaries. Their demise appears to be 
the result of a combination of disease and human 
activities that have reduced the quality of estuarine 
waters. Despite relatively limited information on the 
ecological functions of these habitats in New Zealand, 
historical information suggests that loss of seagrass 

New Zealand 

Photographers negotiating the tidal channels near New Brighton in 
the Avon-Heathcote Estuary in the early 1900s. The elevated intertidal 
banks are clearly vegetated with extensive stands of Zostera 

has had similarly dramatic effects on the distribution 
and abundance of invertebrates, fishes and other 
estuarine wildlife that depend upon them, including 
some species of commercial significance. The high 
turbidity of many New Zealand estuaries - caused by a 
combination of natural topography and changes in land 
use - means that restoration efforts are likely to be long 
term and broad based, necessitating changes in land 
and catchment management. Immediate conservation 
is, therefore, best focused on the relatively few areas 
where there are large, persistent meadows. There are, 
however, promising signs of improving water quality in 
a number of estuaries and of the recent expansion of 
seagrass habitats in some areas. 


Preparation of the review and attendance at the Global Seagrass 
Workshop was supported by a Technical Participatory Programme grant 
from the International Science and Technology Linkages Fund. Thanks 
are due to Diane Gardiner {Ministry of Research, Science and 
Technology), Megan Linwood [Ministry for the Environment) and Rick 
Pridmore (National Institute of Water and Atmospheric Research Ltd) for 
facilitating this. Valuable information from, and discussions with, Mark 
Morrison, Anne-Maree Schwarz [NIWA], Paul Gillespie (Cawthron 
Institute], Stephanie Turner (Environment Waikato) and Don Les 
(University of Connecticut] improved the content of the manuscript. 


Graeme Inglis, National Institute of Water and Atmospheric Research 
Ltd, P.0. Box 8602, Christchurch, New Zealand. Tel: +64 {0]3 348 8987. 
Fax: +64 (0}3 348 5548, E-mail: 











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13 The seagrasses of 


of Thailand and the Andaman Sea, and coastal 

habitats support abundant populations of 
commercial fish and associated nearshore fisheries. 
Seagrasses occur in many locations along the Thai 
shoreline. The occurrence, community structure and 
biomass of seagrasses have been studied at different 
locations in 19 provinces along the coastal areas of the 
Gulf of Thailand and the Andaman Sea. Among the 12 
species of seagrasses found in Thailand, Halophila 
ovalis is the most widely distributed, because of its 
ability to grow in different habitats. Enhalus acoroides, 
the largest species, is also common in the major 
seagrass areas. Seagrasses are more abundant in the 
Andaman Sea than in the Gulf of Thailand. 

Te coastline of Thailand is 2583 km along the Gulf 


Most of the seagrass beds are multispecies beds 
located in enclosed or semi-enclosed embayments 
from the intertidal area to 5 m in depth depending on 
seagrass species, chemical and physical factors. 
Distribution and habitat of the 12 seagrass species in 
Thailand is summarized in Table 13.1. Seven species 
are widespread in both the Gulf of Thailand and the 
Andaman Sea. Enhalus acoroides occurs in brackish 
water canals down to the lower intertidal and subtidal 
zones on mud, muddy sand and sandy coral substrates; 
Thalassia hemprichii grows on muddy sand or 
fragmented dead coral substrates in the upper littoral 
zone or coral sand substrate in subtidal areas; 
Halophila beccarii grows on mud or muddy sand 
substrates in estuarine and coastal areas in the 
intertidal zone; Halophila decipiens was previously 
thought only to occur in waters 9-36 m in depth but has 
been found in the intertidal areas where it is exposed 
during low tides; Halophila ovalis is found growing on 
various substrates such as mud, muddy sand and dead 
coral fragments in the upper littoral to subtidal areas; 
Halodule pinifolia and Halodule uninervis both grow in 

C. Supanwanid 
K. Lewmanomont 

sandy or muddy sand substrates from the upper littoral 
to subtidal areas. Two species occur only in the Gulf of 
Thailand: Halophila minor which grows on muddy sand 
in the intertidal zone and Ruppia maritima in mangrove 
areas or brackish water ponds. Cymodocea serrulata, 
which grows on muddy sand, fine sand or sand with 
coral rubble substrates in the intertidal zone, occurs in 
both regions but is mainly distributed along the 
Andaman Sea coastline. Two species are found in the 
Andaman Sea and not the Gulf: Cymodocea rotundata, 
which occupies the lower littoral zone on muddy sand 
area or sandy bottom mixed with dead coral fragments 
and Syringodium isoetifolium which occurs densely in 
subtidal areas on fine sediment. 

A total of 68.5 km’ along the coast of Thailand is 
known to be covered by seagrasses, but actual 
coverage must be much greater given the lack of 
measurements in 11 of the 24 locations in Table 13.1. 
Seagrass distribution is more extensive in the Andaman 
Sea than in the Gulf of Thailand. 

The four most important seagrass beds in 
Thailand are Haad Chao Mai National Park, in Trang 
province on the southern coast of the Andaman Sea and 
just north of Malaysia, Ko Talibong (Talibong Island), 
also in Trang province, Kung Krabane Bay, in 
Chanthaburi province on the eastern coast of the Gulf of 
Thailand near to Cambodia, and Ko Samui (Samui 
Island), in Surat Thani province, and part of the 
southern coast of the Gulf of Thailand. 

The seagrass beds at Haad Chao Mai National 
Park, Trang province are the largest of these seagrass 
beds and cover 18 km’, with the highest species 
diversity for a single area in Thailand”. The beds cover 
a small area around a peninsula called Khao Bae Na 
and a larger area between the islands of Ko Muk and 
Laem Yong Lum on the mainland. There are nine 
species in this area: Enhalus acoroides, Thalassia 
hemprichii, Halophila decipiens, Halophila ovalis, 
Halodule pinifolia, Halodule uninervis, Cymodocea 

rotundata, Cymodocea serrulata and Syringodium 
isoetifolium. Halophila decipiens is considered to be 
a deepwater seagrass species in Thailand. However 
this species occurs in the intertidal zone at Khao Bae 
Na and pure stands of Halophila decipiens are 
therefore exposed during low tide down to the depths of 
5m"! Until recently the only available information on 
the seagrass beds at Haad Chao Mai National Park was 
qualitative and restricted to the intertidal zone, but in 
2000 the distribution and biomass of seagrasses over 
the entire subtidal and intertidal bed was 
investigated’. The biomass was highest at shallower 
depths [<2 m) all along the coastline. Enhalus 
acoroides was the most abundant species, followed by 
Halophila ovalis and Thalassia hemprichii. Both 
Halophila ovalis and Thalassia hemprichii were 
dominant at the upper intertidal area and formed 
monospecific patches in sand dunes and tide pools 
respectively. Average above-ground biomass of 
seagrasses in the intertidal area (15 g/m’) was 1.5 
times greater than the biomass of subtidal seagrass 
beds (10 g/m’). Enhalus acoroides was the most 
dominant species in the subtidal and lower intertidal 
zones'. The sedimentation rate inside the Enhalus 
acoroides beds was greater than those inside the 
Thalassia hemprichii and Halophila ovalis beds 
because of the shape and size of the Enhalus acoroides 
plants". It has been suggested that distribution of 
seagrass beds in this area is primarily controlled by the 
physical conditions of the local environment, principally 
the roughness of weather during the monsoon season 
and the amount of shelter available at different 
locations'"’. This is also true for the seagrass beds at 
Ko Talibong. The strong southwest waves during the 
monsoon season (May-October) induces instability of 
bottom sediments and high turbidity preventing 
seagrass settlement and growth in the area directly 
facing offshore waters'. Consequently seagrasses 
only flourish in areas sheltered by the offshore islands. 

At the muddy flat of Ko Talibong, 15 km from the 
southern end of the Haad Chao Mai National Park bed, 
7.0 km? of nine seagrass species are distributed along 
the northern, eastern and southeastern coasts of this 
island. This bed is very important as a feeding ground 
for the dugong (Dugong dugon)"”. One hundred and 
twenty-three dugongs were found in Haad Chao Mai 
National Park and Ko Talibong seagrass beds in 2001, 
with the largest herd size being 53 dugongs in the Ko 
Talibong seagrass bed'"”. 

Compared to the seagrass bed at Haad Chao Mai 
National Park, the seagrass bed at Ko Talibong is highly 
affected by siltation from the Trang River. These 
seagrasses grow in a highly turbid environment with a 
transparency of about 1-2 m on mud and muddy sand 
substrates. As a result the maximum depth of seagrass 


5 104° E 
Chon Bun 
*» @Chanthabun 

Kung Krabane Bay -9itat 

MYANMAR » ®>rachuab Khiri Khan 
Koh Kram 


© Chumphon 

# Ranong 


© Ko Samui 

F surat Thani 
THAILAND Gulf of Thailand 

Nakhon Si os 
Thammarat ® 

Phuket i tren! 
} 3 Tran, 

ig Phatthalun: 
Phangnga Bay .° 3 

Haad Chao Mai 2 

National Park Pattani 
Libong Island oatun \ 
Ko Talibong eT ‘e Narathiwat 


0 50 100 150 Kilometers 

Map 13.1 

is limited to 2.5 m''". At the eastern end of the island, 
seagrasses grow on muddy flats and are exposed to the 
air during low tide. Nine seagrass species were found: 
Enhalus acoroides, Thalassia hemprichii, Halophila 
beccarii, Halophila ovalis, Halodule pinifolia, Halodule 
uninervis, Cymodocea rotundata, Cymodocea serrulata 
and Syringodium isoetifolium"”. Enhalus acoroides and 
Halophila ovalis were the dominant species in intertidal 
flats while Halophila ovalis was widely distributed in 
the subtidal area to the southeast of the island. 

In the Gulf of Thailand, two major seagrass beds 
are located in the almost enclosed Kung Krabane Bay 
in Chanthaburi province and Ko Samui in Surat Thani 
province’ “*”!. Kung Krabane Bay has a small narrow 
opening to the sea and an area of approximately 15 km* 
which is surrounded by mangroves and shrimp ponds. 
Five species of seagrasses grow here: Enhalus 
acoroides, Halophila decipiens, Halophila minor, 
Halophila ovalis and Halodule pinifolia, and cover 
7.0 km?":'*" The deepest part of this bay does not 
exceed 6 m. Enhalus acoroides and Halodule pinifolia 
were the two dominant species among the five’. 

Ko Samui Is the largest island on the west coast 
of the Gulf of Thailand and a major destination for 
foreign tourists. Five species of seagrasses grow in 
beds that almost completely surround the island: 
Halodule uninervis, Halophila minor, Halophila ovalis, 
Halophila decipiens and Enhalus acoroides cover a 
total area of 7.7 km’ and grow in association with 
corals, mainly Acropora spp. and massive species of 
coral, scattered around the island. Most of the seagrass 




Table 13.1 
Occurrence of seagrass species in Thailand 

seagrass area 
Chon Buri 7 
Rayong v 
Makampom Bay 
Kung Krabane Bay 
Prachuab Khiri Khan 
Surat Thani 
Ko Samui 
Nakhon Si Thammarat 
Haad Chao Mai National Park 
Ko Talibong 


Seagrass species 
Hm Ho 



No. of Area 
Cs Si Rm species {km’) 
if v 6 id 

Hp Hu 




Notes: Ea Enhalus acoroides; Th Thalassia hemprichii; Hb Halophila beccarii; Hd Halophila decipiens; Hm Halophila minor, Ho Halophila ovalis; 
Hp Halodule pinifolia, Hu Halodule uninervis; Cr Cymodocea rotundata; Cs Cymodocea serrulata; Si Syringodium isoetifolium,; Rm Ruppia 

id insufficient data. 

Source: Various sources' 

areas were formed outside the area of living corals or 
on reef flats inside the coral reef. Enhalus acoroides 
grows on coarse substrates ranging from medium and 
coarse sand to coral rubbles at a depth of 0.5-1.0 m. 
Halodule uninervis, Halophila ovalis, Halophila minor 
and Halophila decipiens are distributed on fine to 
medium sand at 2.5-7.0 m in depth.” 


The first report of Halophila ovalis and Halodule 
uninervis in Thai water was made in 1902 when 
Halophila decipiens was also described as a new 
species. There were no further reports until 1970 when 
den Hartog found five species in Thailand: Cymodocea 
rotundata, Thalassia hemprichii, Halophila ovalis, 
Halophila ovata and Halophila decipiens". \In 1976, 

Lewmanomont reported the occurrence of seagrasses 
belonging to Halophila, Enhalus and Cymodocea in the 
mangrove areas’. Christensen and Anderson found 
two seagrass species in Surin Island in 1977". Two 
species were recorded in Koh Kram in Chon Buri 
province”! After this, many reports were published on 
the occurrence, community structure, biomass and area 
of seagrasses. Many studies on the ecology and biology 
of seagrasses have been initiated under the ASEAN- 
Australia Marine Science project since 1988”. 

For Thai people, the main importance of 
seagrasses is their role as fishing grounds and as 
habitats for many commercially important species and 
endangered marine mammals, but the value of 
seagrasses to provincial and national economies has 
not been quantified. Indirect uses of seagrasses in 

Thailand include their role in coastal protection and as 
nursery grounds for marine species. 

Before 1999 there was no information on the 
importance of seagrasses in coastal protection in 
Thailand. Then studies on the water flow and 
hydrological factors in seagrass beds at Haad Chao Mai 
National Park were conducted. The studies showed that 
the intensity of bottom water movement in seagrass 
beds at lower depths was less than that at the upper 
depths. This study demonstrated the effectiveness with 
which Enhalus acoro/des beds retard the intensity of 
water motion: current speed inside the Enhalus 
acoroides beds was 15 cm/s on the seafloor and 25 
cm/s at 0.5 m in depth. This was a slower movement of 
water than inside the other seagrass beds, and over 
bare sand where currents speeds were 22.5 cm/s and 
35 cm/s on the seafloor and at 0.5 m depth, respectively. 
The width and length of Enhalus acoroides blades is the 
greatest among the seagrass species of Thailand, and 
the blades not only greatly reduce the rate of water flow 
under and over the meadow but also induce a higher 
sedimentation rate as a result. In this way, the seagrass 
beds at Haad Chao Mai National Park create and 

Case Study 13.1 

In Thailand, most fishermen and local people know 
that seagrass is an important food for the dugongs 
(Dugong dugon). The dugong in Thailand is an 
endangered species and Is protected under the Thai 
Fishery Act 1947. 

Before the first aerial survey for dugong in 
1992, not many Thais knew what dugongs and 
seagrasses were. During the first survey in 1993, 
dugongs were found near the seagrass bed in Trang 
Province and the Royal Forestry Department 
announced that this was the last herd of dugong in 
Thailand’. However, dugongs may still exist on the 
eastern coast of the Gulf of Thailand”. Fishermen in 

Rayong province have seen dugongs and their 

feeding trails on small seagrass species. 

More dugong feeding trails on Halophila ovalis 
at Haad Chao Mai National Park were reported in 
1996"! At that time, Thai people believed that 
dugongs preferred feeding on small seagrass 
species. In 1998, the study on dugong grazing on 
Halophila ovalis beds at Haad Chao Mai National 
Park was carried out. It was reported that in a 100 x 
100 m quadrat, one dugong could produce 14.9 
feeding trails (5.1 m*/day). The estimated grazing 
rate of Halophila ovalis by a dugong was 1.1 kg dry 


maintain a unique physical environment in terms of 
water motion and sedimentation which protects the 
coastline from the adverse effects of high wave action 
during the monsoon season”. 

Thai seagrass beds are a nursery ground for 
juvenile fishes and other marine animals. At Haad Chao 
Mai National Park, 30 families of fish larvae have been 
recorded in the nearshore seagrass bed. The 
abundance of fish larvae in the seagrass bed, at 2064 
individuals/1000 m*, was higher than in open sandy 
areas, with 1217 individuals/1000 m*. Economically 
important fish larvae found in this area were 
Carangidae, Nemipteridae, Engraulidae, Mullidae and 
Callionymidae”*. At Haad Chao Mai National Park 
seagrass bed, juveniles of the Malabar grouper, 
Epinephelus malabaricus, were collected by small fish 
traps and cultured in net cages in the canals near the 
seagrass bed”. Twenty-two species of juvenile fishes 
were reported in the seagrass bed at Kung Krabane 
Bay, Chanthaburi province. Among these, Serranidae 
are the most abundant and are also the most important 
species for fisheries. From October to December, 
fishermen collect juveniles of Serranidae species 

weight, 13.0 kg wet weight/day. Recently, other 
seagrass species were found in the stomach content 
of dugongs in Trang province. The species included 
Halodule pinifolia, Halodule uninervis, Halophila 
ovalis, Cymodocea rotundata, Cymodocea serrulata, 
Syringodium isoetifolium, Thalassia hemprichii and 
Enhalus acoroides*”. 

The dugongs in the Andaman Sea are a 
flagship species based on their specialized relation- 
ship with seagrasses and they are further evidence 
of the value and importance of the seagrass 
ecosystem. Recent surveys have shown that more 
than 60 percent of the people along the Andaman 
Sea appreciate the importance of the dugongs and 

Dugongs and seagrass on a Thai stamp. 




{approximately 2.5 cm in length] in the morning using 
scoop nets, and culture them in net cages until they 
grow to marketable size, when each individual weighs 
more than 0.8-1.5 kg'”. 

Seagrass beds in Thailand are very important 
areas for fisheries, over and above their role as nursery 
areas, with both demersal and highly mobile species of 
fish being harvested from seagrass areas throughout 
the country. At least 318 species representing 51 
families have been identified in seagrass beds in ASEAN 
countries. They have economic value mainly as food and 
aquarium specimens”. In Thailand the diversity of fish 
is lower in seagrass beds in the Gulf of Thailand (where 
38 species of fishes from 29 families have been 
recorded from six seagrass beds’) than in the 
Andaman Sea (where 78 species of fishes from 46 
families have been recorded from the seagrass beds at 
Haad Chao Mai National Park]. Many species are very 
important in terms of economic value such as 
Epinephelus malabaricus, orange-spotted grouper 
(Epinephelus coioides), great barracuda (Sphyraena 
barracuda), squaretail mullet (Liza vaigiensis), brown- 
stripe red snapper (Lutjanus vitta), Russell's snapper 
(Lutjanus russell], mangrove red snapper (Lutjanus 
argentimaculatus}, oriental sweetlips (Plectorhinchus 
orientalis), silver sillago (Sillago sihama) and Indian 
mackerel (Rastrelliger kanagurta)””. 

In addition to the fishes in the seagrass area, 
crabs and sea cucumbers are also important to 
fisheries. Since 1998, local fishermen have been 
collecting sea cucumbers from many seagrass beds in 
summer, during low tide. After drying the sea 
cucumbers, the fishermen sell them to Malaysian 
buyers. At present, three species of sea cucumber have 
been harvested, namely, Holothuria scabra, Holothuria 
atra and Bohadschia marmorata. Fresh sea cucumber 
costs US$12-15 (500-600 Baht) per kg while the dried 
ones cost US$25 per kg’. Eighty percent of the crabs 
exported from Thailand are portunids, mainly Portunus 
pelagicus, coming mostly from seagrass areas." 

Direct use of seagrass is less apparent in Thailand 
although the seeds of Enhalus acoroides are eaten by 
Thai fishermen. They believe that someone who has a 
chance to eat the seeds of Enhalus acoroides will be 
lucky. However, they do not like to harvest the fruits of 
Enhalus acoroides for food because of the time 
necessary to collect enough seeds. Local people in 
some areas in Thailand use dry seagrass leaves and 
rhizomes for the treatment of diarrhea. At present, 
extracts from many species are being screened for 
biological properties. For example a group of research- 
ers from Kasetsart University has been testing crude 
seagrass extracts and conducting five bioassays (anti- 
bacterial, antifungal, cytotoxicity, antialgal and toxicity 
tests] on these extracts. 


It is very difficult to estimate the seagrass loss in 
Thailand because there are no reports on historical 
coverage or loss. Most of the studies on seagrasses in 
Thailand were conducted recently and over very short 
periods of one to two years. There has been no long- 
term monitoring in the country. Even the present 
seagrass coverage cannot be completely estimated. 
However there is evidence showing that a small 
seagrass bed at Khao Bae Na in Haad Chao Mai 
National Park has been covered by sand. 

Khao Bae Na is a small embayment of flat sand 
which had a dense Halophila ovalis meadow extending 
over approximately 30000 m’ and served in the past as 
a feeding ground for dugongs. The feeding trails of 
dugongs were clearly seen during low tide. Some 
Cymodocea rotundata, Halophila decipiens and small 
patches of Enhalus acoroides occurred in this area. 
Tidal level of the meadow was about 1.8 m above mean 
lower low water’. Since the monsoon season in 2000, 
this seagrass bed has been covered with a high level of 
sediment. Only small patches of Halophila ovalis and 
Cymodocea rotundata have survived and their 
distributions have been limited by the high 
sedimentation rate. It is thought that the dugongs have 
moved their feeding grounds to Ko Muk and Talibong 
Island seagrass beds. 

On 20 January 2002, damage to the seagrasses at 
Baan Pak Krok in Phuket by the use of mechanized 
push seines was reported in the press, but the area 
affected was not estimated. The Natural Resource 
Conservation Group of Baan Pak Krok requested the 
government to strengthen law enforcement. There is 
other anecdotal evidence of damage to seagrass areas 
in Thailand but it would be impossible to determine the 
actual loss. 


Seagrasses in Thailand are threatened by a 
combination of illegal fisheries and fishing practices, 
and land-based activities, especially mining. The 
destruction of seagrass beds is caused by fishing gear 
such as small-mesh beach seines and mechanized 
push seines. 

Before 1992, the local fishermen in five villages 
near Haad Chao Mai National Park used mechanized 
push seines that decreased the number of marine 
animals and seagrass area. Paradoxically the 
fishermen’s income also decreased while the use of 
these illegal fishing gears increased. They started to 
fish by using dynamite and cyanide in the seagrass bed. 
After 1992, the Royal Forestry Department announced 
the occurrence of dugong in Haad Chao Mai National 
Park, and a mass media campaign helped to spread 
awareness of dugong and seagrass conservation in 

Thailand. Local organizations implemented dugong and 
seagrass conservation projects to persuade local 
fishermen to stop using beach and push seines in 
seagrass areas. They can now only use traps for fishing. 
One year later, the seagrass bed at Haad Chao Mai 
National Park had increased in size and the fishermen’s 
income had increased because of larger catches from 
within the protected seagrass areas. However, the Royal 
Forestry Department still found mechanized push seine 
trails in other seagrass areas”. 

In Thailand, tin mining is centered in Phuket, 
Phangnga and Ranong provinces. It has been 
suggested that sediments from tin mining in Phuket 
cause chronic problems for seagrass beds in Phuket 
and Phangnga provinces. Mining activities have now 
decreased drastically in most areas, but the seagrasses 
are still affected by other activities, such as land 
development resulting in landfill, open topsoil on roads 
and construction on hill slopes”. 

A major threat to seagrasses in Thailand is 
reduced water clarity in many areas resulting from 
upland clearing, development along rivers and 
destruction of mangrove forests. 

In Thailand, there are only two seagrass protected 
areas. These are Haad Chao Mai National Park and 
Libong Island Non-hunting Area. Haad Chao Mai 
National Park is administered by the Royal Forestry 
Department under the auspices of the Marine National 
Park Division. Haad Chao Mai National Park was 
established in 1981 and encompasses 230.9 km’ - 59 
percent of the area is an aquatic zone. Hunting and 
collecting are forbidden since this is the largest 
seagrass bed with the highest diversity in Thailand. 
Libong Island Non-Hunting Area (Ko Talibong Non- 
Hunting Area) was established in 1960. The only activity 
restricted here is hunting. Seven square kilometers of 
seagrass bed distributed in this area serves as a 
feeding ground for more than 53 dugongs. Most of the 
officers of Libong Island Non-hunting Area are the local 
people of the island. They not only protect the area from 
hunting but also help other local people understand the 
importance of seagrasses to the marine environment. 
There have been several other policy initiatives 
designed, in part, to conserve seagrasses. In 1972, the 
Ministry of Agriculture and Co-operatives declared that 
all mechanized fishing gears were prohibited within 
3000 meters of the coastline in all coastal provinces. In 
1993, Trang Provincial Notification was empowered 
under Fisheries Act B.E. 2490 (Fisheries Act 1947] 
Section 32” to declare that trawlers, mechanized push 
seines, beach seines and gill nets were prohibited in 
Haad Chao Mai National Park seagrass bed and at Ko 
Talibong. In 1997, the Ministry of Agriculture and Co- 


Dugong feeding trails on Halophila ovalis at Haad Chao Mai 
National Park 

Seeds of Enhalus acoroides 

operatives declared the prohibition of trawlers, 
mechanized push seines, purse-seines and nets in the 
area along Phangnga Bay which includes Phuket, 
Phangnga and Krabi coastlines. 

In 1998, the Office of Environmental Policy and 
Planning proposed policies for the management of 
seagrass resources including: 

() accelerated management and control of water 

) increasing efficiency in management of seagrass 
conservation through landuse planning; 


Photo: C. Supanwanid 

Photo: J.S. Bujang 



) support for studies on seagrass research and 

fo) campaigns to heighten and improve public 
awareness of the importance of conserving 
seagrasses, at all levels of the community; 

) review and adjustment of laws, regulations and 
enforcement concerning seagrasses so that they 
work more efficiently by recognizing the import- 
ant roles of local authorities and communities; 

) the monitoring of the status and problems of the 
seagrass beds, with the cooperation of central 
government, local authorities and local people”. 

So far seagrass monitoring, restoration and 
conservation in Thailand has not been widely 
successful in the long term because of a lack of 
funding and a suitable methodology. Law enforcement 
alone has not led to the successful protection of the 
seagrass ecosystem. It is necessary to involve local 
people through information and education. A non- 


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We are grateful to Dr F.T. Short and Dr R.G. Coles for 
their great support. Sincere thanks go to Assistant Professor Dr C. 
Meksampan, P. Wisespongpand, S. Putchakarn, S. Wongworalak, 
S. Pitaksintorn, K. Adulyanukosol, Assistant Professor Dr S. 
Satumanatpan and N. Suksunthon for their information and help. 


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Seagrass fish fauna in the Gulf of Thailand. In: Chou LM, 

Wilkinson CR leds) Third ASEAN Science and Technology 

Week Conference Proceedings, Vol. 6, Marine Science: 

Living Coastal Resources. National University of Singapore 

and National Science and Technology Board, Singapore. 

pp 301-306. 

Putchakarn S. Personal communication. 

Sea Aueng S, Witayasak W, Lukanawakulra R, Pearkwisak W, 
O'Sullivan P [1993]. A survey of dugong in seagrass bed at 
Changwat Trang. In: The 31st Kasetsart University Annual 
Conference, Kasetsart University, Bangkok. pp 363-368. 
Nateekanjanalarp S, Sudara S [1994]. Dugong protection 
awareness: An approach for coastal conservation. In: Sudara S, 
Wilkinson CR, Ming CL (eds) Third ASEAN-Australia 

Symposium on Living Coastal Resources, 16-20 May 1994. 
Department of Marine Science, Chulalongkorn University, Bangkok. 
pp 915-525. 

Pitaksintorn S. Personal communication. 

Supanwanid C [1996]. Recovery of the seagrass Halophila ovalis 
after grazing by dugong. In: Kuo J, Phillips RC, Walker DI, Kirkman 
H leds) Seagrass Biology: Proceedings of an International 
Workshop, 25-29 January 1996, Rottnest Island, Western Australia. 
University of Western Australia, Nedlands, Western Australia. pp 

Mukai H, Aioi K, Lewmanomont K, Matsumasa M, Nakaoka M, 
Nojima S, Supanwanid C, Suzuki T, Toyohara T [1999]. Dugong 
grazing on Halophila beds in Haad Chao Mai National Park, Trang 
Province, Thailand: How many dugongs can survive? In: Koike | {ed] 
Effects of Grazing and Disturbance by Dugongs and Turtles on 
Tropical Seagrass Ecosystem. University of Tokyo, Tokyo. 

pp 239-254. 

Adulyanukosol K, Poovachiranon S, Natakuathung P [2001]. 
Analysis of stomach contents of dugongs [Dugong dugon] from 
Trang Province. Fishery Gazette 54(2): 129-137 {in Thail. 

Hines E [2000]. Population and Habitat Assessment of the Dugong 
(Dugong dugon) off the Andaman Coast of Thailand. Final report 
submitted to the Ocean Park Conservation Foundation, Hong Kong. 
Satumanatpan S, Sudara S, Navanugraha C [2000]. State of the 
seagrass beds in Thailand. Biologia Marina Mediterranea 7(2): 




14 The seagrasses of 


alaysia’s coastline is around 4800 km long, 
M stretching along the Malay Peninsula, Sabah 

and Sarawak, bounding much of the southern 
part of the South China Sea. In and adjacent to this 
coastline are three major coastal ecosystems - 
mangroves, coral reefs and, less well known, 
seagrasses. Corals are found on the outer edge of the 
coastal zone while mangroves are on the inner edge. In 
general, coastal areas between mangroves and corals, 
from low-tide level to the coral reef fringe, form the 
habitats for seagrasses in Malaysia. Seagrasses are 
also found around offshore islands with fringing corals. 
Here they are usually found in the outer region between 
the corals and the semi-open sea. The earliest account 
of seagrasses in the shallow bays all around the coast 
of Peninsular Malaysia dates back to 1924". 
Information on seagrasses is scattered and appears in 
a number of books, scientific publications and 
monographs” "". These have been largely taxonomic in 
nature and list habitats of at least seven species of 
seagrasses: Enhalus acoroides (then referred to as 
Enhalus koenigii by Ridley and Holttum), Halophila 
ovalis, Halophila minor (referred to as Halophila ovata 
by Henderson], Halophila spinulosa, Halodule uninervis 
{then referred to as Diplanthera uninervis), Thalassia 
hemprichii and Ruppia maritima. 

In recent years more research has been carried 
out on seagrasses in Malaysia. Consequently there are 
now a number of reports in the literature that describe 
the extent and richness of flora’ and fauna!’?:*”*" in 
Malaysian seagrass beds. Unlike other terrestrial 
communities that can be lived in, managed or exploited, 
seagrasses offer only a few direct uses. The ecological 
role and importance of seagrasses has not been fully 
understood. Much more effort has been spent on 
quantifying and managing mangroves and corals. 
Mangrove reserves have been established and coral 
reefs are protected and conserved in marine parks and 
marine protected areas. There are guidelines and 

J.S. Bujang 
M.H. Zakaria 

policies governing the conservation and management 
of mangroves by the National Mangrove Committee”” 
and corals under the Fisheries Act 1985. However the 
importance of seagrasses at local and national levels, 
and from the standpoint of conservation, has received 
far less attention. There are no specific reserves or 
legislation for seagrasses. Given the importance of 
seagrass as fisheries habitat, nursery and feeding 
grounds in Malaysia, this neglected and relatively 
lesser known resource must be afforded the same 
priority and be as well managed as mangroves and 
corals to provide for future renewable resource 
utilization, education and training, science and 
research, conservation and protection. 


The majority of seagrasses in Malaysia are restricted to 
sheltered situations in the shallow intertidal associated 
ecosystem, semi-enclosed lagoons and also in subtidal 
zones. In these areas they sometimes form diverse 
extensive communities. The overview of the seagrass 
distribution and description in this section is given 
separately for Peninsular and East Malaysia (Sabah). 
We include specific examples to illustrate the types of 
seagrass bed found in Malaysia. 

Peninsular Malaysia 

Along the west coast, patches of mixed species 
seagrass communities usually occur on substrates 
from the sandy mud to sand-covered corals in the 
extreme northern region along the coast of Langkawi 
Island, Kedah, to the central region of Port Dickson, 
Negri Sembilan", extending as far as Pulau Serimbun, 
Malacca’. The Port Dickson area, at Teluk Kemang, is 
the only area in mainland Peninsular Malaysia that has 
intertidal seagrass on reef platform. In the southern 
region, around the Sungai Pulai area, Johore, mixed 
species seagrass beds exist at depths of 2-3 m on both 
sandy mud banks of the mangrove estuary” and 

Pengkalan Nangka 
seca Pulau Perhentian 
ov Pulau Redang 

« Gong Batu 

* Paka CHINA 
*~ Kemasik SEA 

= Telaga Simpul 


Strait of 

Malacca © Kuala Lumpur Pulau Tengah 

® Pulau Tioman 

Teluk 4A Port Dickson 


=> Pulau Tinggi 
Pulau Pulau Sibu 

ee” Merambong, 

(Sumatra) Adang Laut 

50 100 150 Kilometers 

Map 14.1 
Peninsular Malaysia 

calcareous sandy mud_ subtidal shoals _ of 
Merambong'”, Tanjung Adang Darat' and Tanjung 
Adang Laut”. These subtidal shoals, at depths of 

2-2.7 m, support nine species (Enhalus acoroides, 
Halophila ovalis, Halophila minor, Halophila spinulosa, 
Thalassia hemprichii, Cymodocea serrulata, Halodule 
pinifolia, Halodule uninervis, Syringodium isoetifolium) 
of seagrasses, the highest species number for any 
locality in Peninsular Malaysia or East Malaysia’. 
These beds measure 1-1.2 km in length and 100-200 m 
in width according to estimates based on the visible 
portion exposed several times in a year by low tides. 
This is therefore probably the largest single seagrass 
bed in Peninsular Malaysia. The south has a greater 
diversity of seagrasses than the northern region with 
just three species (Halophila ovalis, Cymodocea 
serrulata and Halodule uninervis) in Tanjung Rhu and 
Pantai Penarak in the north. 

Intertidal areas of the eastern coastline are 
devoid of seagrasses. Beds of two species, Halophila 
beccarii and Halodule pinifolia, inhabit the fine sand 
substrate of the shallow inland coastal lagoons from 
Pengkalan Nangka, Kelantan, to Paka, Terengganu, 
while Halodule pinifolia and Halophila ovalis inhabit a 
similar substrate type at Gong Batu and Merchang. 
Monospecific beds of Halodule pinifolia were found at 
Kemasik, Terengganu, and pure stands of Halophila 
beccarii grew on the mud flat of the mangroves in 
Kemaman, Terengganu. Monospecific beds of Halodule 
pinifolia, Halophila decipiens and mixed species 
seagrass beds occur in the waters of the offshore 


SOUTH 20 40 60 80100 Kilometers wy | 
SEA Bak-Bak 5 
a = 7N 



Sungai Salut 

*Tunku Abdul Rahman 
~~ Marine Parks 

Turtle Islands 

Pulau_—# B 
Gaya *\ ‘Sungai Mengkabong 
‘ Sepangar Bay 

Pulau Tiga 
' Sabah 

Labuan Island SUN Lahad Datu, 

Pulau Tabawan —* * 

= Pulau Bohay 

Pulau Maganting ~ /Dulang 



116°E Pulau Sipadan 

Map 14.2 

islands with fringing coral reefs such as Pulau Sibu, 
Pulau Tengah, Pulau Besar and Pulau Tinggi’, Pulau 
Redang and Pulau Perhentian™! and Pulau Tioman™. 
Seagrasses are usually found in the outer region 
between the corals and the semi-open sea. 

East Malaysia 

The west and southeastern coasts of Sabah harbor 
mixed species seagrass beds in the intertidal zone 
down to a depth of 2.5 m. Seagrasses grow on 
substrates ranging from sand and muddy sand to coral 
rubble. There are six areas of intertidal mixed 
associations of seagrass and coral reef along the west 
coast at Bak-Bak, Tanjung Mengayau, Sungai Salut, 
Sungai Mengkabong, Sepangar Bay and Pulau Gaya. 
The four isolated offshore islands of Pulau Maganting, 
Pulau Tabawan, Pulau Bohay Dulang and Pulau 
Sipadan along the southeastern coast have subtidal 
seagrasses growing on coral rubble! 77°»), 

In Sarawak, other than records of herbarium 
specimens of Halophila beccarii, collected by Beccari in 
Sungai Bintulu”'”’, and Halophila decipiens collected at 
Pulau Talang Talang, Semantan™', nothing much is 
known about the seagrass habitats, distribution and 
species composition. 


Peninsular Malaysia 

The distribution of seagrasses in Peninsular Malaysia 
has been detailed in various publications!” ''>"67)_ A 
very broad distinction can be made between the 
seagrass distribution of the west and east coasts. 
Differences in the available habitats and prevailing 
environmental characteristics along the east and west 
coasts probably explain these distributions. On the west 
coast seagrasses occur in the sandy mud sediments of 




shallow coastal waters while on the east coast the 
coastline is fringed with sandy to rocky areas which are 
not suitable for the growth of seagrasses. On the east 
coast seagrasses inhabit sandy mud lagoons, behind 
the sand ridges in areas sheltered from the open sea. 
Seagrasses are also found around relatively calm 
offshore eastern islands with fringing reefs such as 
Pulau Redang, Pulau Perhentian, Pulau Tengah, Pulau 
Sibu, Pulau Tinggi and Pulau Besar. The west coast of 
Peninsular Malaysia does not generally experience 
strong wave action, whereas the east coast is exposed 
annually to the northeast monsoon from November to 

Clarity of water and sufficient light irradiance play 
a significant role in the depth distribution of the 
seagrasses. Coastal waters are often turbid or high in 
suspended solids that limit the depth at which most 
seagrasses grow, more so on the western coast of 
Peninsular Malaysia than the east. This is reflected in 
seagrass communities along the west coast which are 
generally found inhabiting the shallow waters at depths 
of less than 4.0 m. Seagrasses on the east coast, how- 
ever, extend to deeper areas, 5.0-7.0 m. Seagrasses 
will colonize greater depth if the water is clear. By way 
of comparison, in the clear water of the east coast the 
depth limit for Halophila decipiens ranged from 6 to 
24 m in the Sungai Redang Estuary and Cagar Hutang 
of Pulau Redang, Terengganu, respectively” while in 
the turbid water of the west coast, at Teluk Kemang, 

Port Dickson, it grows at 1.5-3.1 m!”. 

Sabah, East Malaysia 

Seagrass distribution along the west and 
southeastern coasts of Sabah was described by 
Ismail in 1993" and in the Tunku Abdul Rahman 
Marine Parks (Pulau Gaya, Pulau Mamutik, Pulau 
Sulug, Pulau Manukan and Pulau Sapi) by Josephine 
in 1997", Almost all seagrasses are associated with 
degraded coral reef, although a few are associated 
with mangroves and habitats damaged through illegal 
fishing by explosive. There were no broad differences 
regionally with respect to species distribution and 


In Peninsular Malaysia seagrasses (Enhalus acoroides, 
Halophila ovalis}) were apparently locally common all 
around the coast on muddy shores and areas exposed 
at low tide'’*“*”. Historical accounts of the distribution 
of seagrass species at three places in Sabah, Labuan 
Island, Sandakan and Lahad Datu, were given by den 
Hartog in 1970'". Information on their abundance was 
not given. Ismail’ described seagrass habitats that 
were already degraded by human activities in Sabah, 
East Malaysia, in 1993. Since the early reports, which 


indicated extensive seagrass beds, many of the habitats 
(e.g. the west coast of Peninsular Malaysia, East 
Malaysia, Sabah) have been exploited or have 
deteriorated to a greater or lesser extent as a result of 
coastal development, especially in the last 15 years!""""" 
Such phenomena would explain the present seagrass 
distribution, which is no longer extensive, and its patchy 
distribution along the Malaysian coastline!” *”". 

Known uses of seagrasses were few. Burkill” in 
his book, A Dictionary of the Economic Products of the 
Malay Peninsula, mentioned that Ridley recorded in 
1924 that the leaves of Enhalus acoroides were one of 
the chief foods of the dugong, Dugong dugon, which 
was then common in Malaysia. Later the dugong 
became rare because it was hunted for meat and hide”. 
Presently dugongs are found in areas with abundant 
seagrasses such as Pulau Sibu, Pulau Tengah, Pulau 
Besar and Pulau Tinggi on the east coast and around 
Merambong, Tanjung Adang Darat and Tanjung Adang 
Laut shoals of Sungai Pulai, Johore. Enhalus acoroides 
fruits are edible’) and the coastal communities of 
Sungai Pulai, Johore, still collect them for con- 
sumption. In addition the softer parts of Enhalus 
acoroides form fibers that are made into fishing nets. 
Ruppia maritima plants are used in fish ponds to aid in 
the aeration of the water, and the milk fish (Chanos 
spp.) feeds on it. This functional role, though 
mentioned, has not been observed in Peninsular 
Malaysia, and is probably based on observations made 
in the fishponds of Java, Indonesia”. Ruppia maritima 
is rare in Peninsular Malaysia". 

Other forms of utilization include using seagrass 
areas for fish (Lates calcarifer and Epinephelus 
sexfasciatus) cage farming, for example at Pengkalan 
Nangka, Kelantan, and Gong Batu, Terengganu, which 
started in 1991, or oyster (Saccostrea cacullata) 
farming as at Merchang from 1998'”'. Seagrass areas at 
Pengkalan Nangka, Kelantan, Paka shoal, Terengganu, 
and Tanjung Adang Laut shoal, Johore, are used as 
collection and gleaning sites for food including fishes, 
gastropods (Lambis lambis, Strombus canarium), 
bivalves (Gafrarium sp., Meretrix sp., Modiolus sp.) and 
echinoderms (sea cucumber e.g. Pentacta quadran- 
gularis, Mensamaria intercedens). Gleaning for food in 
seagrass areas associated with coral reefs is 
widespread in Sabah, East Malaysia. 


There is no information in the form of historical maps 
or aerial photographs that can be used to determine 
the loss of seagrass beds over time. The losses 
reported here have been observed during repeated 
visits to the various seagrass sites. On the west coast of 
Peninsular Malaysia, at Port Dickson, localized 
depletion of seagrass (narrow-leaved Halodule 

uninervis and Enhalus acoroides) began in 1994, 
representing about 50 percent of the area originally 
present. This area was heavily utilized as a public 
recreational area. At Teluk Kemang in 1997 there was 
intensive sand mining for reclamation activities in 
mangrove swamps as part of the construction of a 
condominium. This caused the loss of Halophila ovalis 
and Halodule pinifolia in the subtidal seagrass bed of 
Teluk Kemang. Suspended particles in the water 
settled on the leaves of the seagrasses, blocking light 
for photosynthesis and causing considerable stress and 
mortality through burial. The presence of an oil 
refinery, intense shipping activity and frequent oil spills 
in the adjacent waters have also been suggested as 
potential causes for the decline or loss of seagrasses 
along the coastline of Port Dickson. Tar balls in 
significant quantities, frequently washed ashore, were 
evidence of oil spills. In addition, petrogenic 

Case Study 14.1 

At Teluk Kemang, Port Dickson, Negri Sembilan, the 
intertidal community consists of non-uniform 
patches of mixed seagrasses and macroalgae on a 
coral reef platform 1.0-1.5 m deep. Seagrasses grow 
in various substrates, from sand-covered coral to a 
combination of silt, coarse sand and coral rubbles 
(see photograph]. Halophila ovalis is dominant and 
widespread, interspersed with Thalassia hemprichii, 
Cymodocea serrulata, Enhalus acoroides and 
Halodule pinifolia. Syringodium isoetifolium, a rare 
species here, occurs in patches in the sand-filled 
spaces amongst coral rubble areas. Macroalgae 
coexist with these seagrasses. 

The most common, and seasonal, macroalgae 
species are (Chlorophytae] Caulerpa sertularioides, 
Caulerpa prolifera, Caulerpa racemosa, Caulerpa 
lentillifera; (Phaeophytae] Sargassum polycystum, 
Sargassum cristaefolium, Sargassum ilicifolium 
and Padina tetrastomatica; and {Rhodophytae] 
Laurencia corymbosa and Jania decussato- 
dichotoma™. This intertidal community extends into 
the subtidal zone to depths of 3.5 m with a clear 
zonation of seagrass species that are confined to 
sandy mud and silty substrates. Pure stands of 
Halophila ovalis and Halodule pinifolia with isolated 
individuals of Enhalus acoro/des occur at a depth of 
1.5 m. Halophila decipiens grows in small patches at 
a depth of 1.5-2.0 m in association with Halophila 
ovalis and Halodule pinifolia. Slightly deeper, at 2.0- 
3.0 m, Halophila decipiens forms a continuous 
meadow. Occasionally patches of pure Halophila 

hydrocarbons were detected in the water and 

sediments at Teluk Kemang™™”. 

The Sungai Pulai seagrass beds Tanjung Adang 
Laut and Tanjung Adang Darat are diverse and 
extensive, and were only discovered in 1991 and 1994 
respectively, yet by 1998 they were at risk from port 
development involving dredging of shallow passage- 
ways and land reclamation for new facilities, both 
causing an increase in the suspended solids in the 
water column. Localized losses were observed with the 
death of sand-smothered Halophila ovalis clearly 
visible. In addition dense overgrowth of the macroalgae 
Gracilaria coronopifolia and Amphiroa fragilissima 
caused the seagrasses in the area to die back. 
However, recovery occurred with regrowth of sea- 
grasses and the disappearance of the macroalgae. 

On the east coast at Pengkalan Nangka, Kelantan, 
the decline was the result of human activities such as 

ovalis occur at depths of 3.2 to 3.5 m. Morphological 
differences are observed in Halophila ovalis in these 
two communities. Subtidal Halophila ovalis plants 
possess much bigger leaf blades and more cross- 
veins®” than plants of the same species growing in 
the intertidal zone. 

Another conspicuous seagrass is Halophila 
decipiens which occurs at shallow depths of 1.5-3.0 
m'*) Halophila decipiens was previously thought to 
be a deepwater species growing at depths between 
10 mand 30 m!"°173), 

Photo: J.S. Bujang 

The Teluk Kemang seagrass macroalgae community on coral 
reef platform. Seagrasses occupy the sand-filled spaces of the 
coral reef platform, and macroalgae dominated by Sargassum 
spp. inhabit the boulders and coral rubbles. 

Malaysia 155 



the dredging of sand for landfills which have totally 
removed two shoals of Halophila beccarii and Halodule 
pinifolia, representing 30 percent of the total seagrass 
area. At Merchang and Kemasik, Terengganu, the effect 
of wind and resulting wave action on lagoon seagrass is 
reduced by the sheltering presence of the sand ridges. 
Despite this protection, 50-70 percent of Halodule 
pinifolia and Halophila ovalis seagrass beds were 
severely damaged by intense winds, waves and 

Case Study 14.2 

sediment movement during the northeast monsoon 
storms of October 1998 to January 1999. No recovery to 
the original areal extent has been observed yet. Mining 
of sand at Telaga Simpul, Terengganu, in March 1997, 
for the shoreline stabilization and protection of Kuala 
Kemaman village, resulted in high total suspended 
solids in the water column and sedimentation 
smothered the dense Halophila beccarii bed there. The 
bed was transformed to sparse and scattered patches 


The subtidal shoal of Tanjung Adang Laut in the 
Sungai Pulai estuary, Johore, is 1.5-2.7 m below 
mean sea level and is vegetated with seagrasses 
(see photograph)'’. This shoal is one of the feeding 
grounds for dugongs around Sungai Pulai, Johore, 
and their feeding trails can be seen clearly at low 
tides. The shoal is made up of calcareous sandy mud 
substrate and supports a mixed species community 
dominated by Enhalus acoroides, Halophila ovalis 
and Halophila spinulosa. This association occupies 
the middle zone (1.5-1.8 m) and is exposed during 
extreme low spring tides. Cymodocea serrulata, 
Syringodium isoetifolium and Halodule uninervis 
inhabit the deeper, narrow edge zones [1.8-2.1 m]) 
which remain unexposed. 

The edge zone is bare at some places, while at 
others isolated patches of Cymodocea rotundata, 
Halophila spinulosa, Halophila minor or Halodule 
pinifolia occur. In the deeper zone (2.1-2.7 m) 
sparse, isolated patches of Enhalus acoroides and 
Halophila ovalis are found. Enhalus acoroides and 
Halophila ovalis occur at depths of 1.5-1.8 m, and 
are also exposed during low spring tides, but are 
able to withstand short periods of desiccating 
conditions. Cymodocea serrulata and Syringodium 
isoetifolium are less resistant and therefore tend to 
occur in the unexposed edge zone (1.8-2.1 ml. 

This seagrass bed also supports a total of 25 
species of macroalgae. Rhizophytic macroalgae 
such as Avrainvillea erecta, Caulerpa spp. and 
Udotea occidentalis are set into the sandy or sandy 
mud substrates whereas epiphytes such as Bryopsis 
plumosa, Ceramium affine, Chaetomorpha spiralis, 
Cladophora spatentiramea, Cladophora fascicularis, 
Cladophora fuliginosa, Dictyota dichtoma, Hypnea 
cervicornis, Gracilaria coronopifolia, Gracilaria 
fisherii and Gracilaria salicornia are attached 
directly to seagrasses. Species such as Entero- 
morpha calthrata and Gracilaria textorii attach to 
mollusk shells or polycheate tubes. Drift macro- 

algae, such as Acanthophora spicifera, Amphiroa 
rigida, Amphiroa fragilissima, Hypnea esperi and 
Ulva spp. lie loosely amongst the seagrasses. 
Attached (e.g. Gracilaria coronopifolia) and drift 
macroalgae [e.g. Amphiroa fragilissima) form 
important components of this shoal community and 
seasonally, from April to July and in November, the 
seagrass bed is overgrown with them. 

The waters around Tanjung Adang Laut as well 
as those of Tanjung Adang Darat and Merambong 
shoals support the fisheries which feed the 
inhabitants of coastal communities. Seventy-six 
species of fishes [including the Indian anchovy 
Stolephorus indicus, barramundi Lates calcarifer 
and Spanish flag snapper Lutjanus carponotatus) 
and others including prawn (e.g. Penaeus indicus) 
and crabs (Portunus pelagicus and Scylla serrata) 
have been reported in the area'””!. The locals also 
used the shoal as a gleaning site for collection of 
gastropods such as Strombus canarium and Lambis 
lambis and bivalves such as Gafrarium spp. and 
Modiolus spp. 

Photo: J.S. Bujang 

Tanjung Adang Laut subtidal shoal with mixed species 
seagrass community. Nine species of seagrass inhabit the 
calcareous sandy mud substrate of the shoal. 

and Halophila beccarii has been largely replaced by the 
more aggressive Halodule pinifolia which now forms a 
monospecific bed. Standing biomass of Halophila 
beccarii has been dramatically reduced from 0.89-4.34 
g dry weight/m* (shoot density of 2078-6 798/m’) before 
the mining in 1996 to 0.58-0.59 g dry weight/m? (shoot 
density of 758-1 386/m*) from April 1997 until January 
1999. Halodule pinifolia biomass and shoot density 
fluctuated from 10.1 to 56.6 g dry weight/m? and 2145.3 
to 8946/m’ respectively during that period. 

In Sabah, no information on decline or loss of 
seagrasses has been reported. However, symptoms of 
a declining seagrass bed were visible at Sepangar Bay. 
The middle sublittoral belt of Halodule uninervis and 
Cymodocea rotundata was eroded by wave action. Edge 
plants have exposed rhizomes and roots. Sediment 
erosion and instability appear to be implicated in the 
progressive decline of these seagrasses in the shallow 


Information on the total area, extent or size of seagrass 
beds in Malaysia is incomplete. The individual and total 
estimated areas presented [Table 14.1] are for the 
known seagrass areas in Peninsular Malaysia. This is 
an underestimate as seagrass areas in the offshore 
islands are not included. Although Ismail’ has 
reported that seagrass beds in Sabah occur in patches 
ranging in size from 10 m to 150 m in diameter, no 
further data are available, though it is known that, 
compared with Peninsular Malaysia, seagrasses are 
common in Sabah. An approximate estimate for 
seagrass areas in Sabah would be many times that of 
the known seagrass areas in Peninsular Malaysia. 


The Malaysian coastal zone is being subjected to a high 
degree of resource exploitation as well as pollution. 
Seagrass beds grow in shallow, coastal zone waters 
and this renders them susceptible to unplanned and 
unmanaged urban and industrial development. These 
problems are compounded by a lack of environmental 
assessment procedures for developments and lack of 
awareness about the importance of seagrasses. In the 
past, and even at present, losses of seagrass 
communities in the coastal areas of Malaysia caused 
either by natural causes or human activities generally 
Pass unnoticed or unrecorded. States such as Kedah 
and Malacca are undertaking land reclamation and 
expansion programs. Land reclamation and expansion 
in Johore is occurring for the development of new port 
facilities. With more expansion planned, the future 
intention is to completely reclaim the stretch of 
seagrass beds of Merambong-Tanjung Adang shoals, 
the feeding ground of dugongs. Sourcing for sand on 


the east coast is a common activity for landfill and 
shoreline stabilization projects. Dredging is being 
carried out in the Halophila beccarii and Halodule 
pinifolia beds of Pengkalan Nangka, Paka shoal and 
Telaga Simpul. This dredging will lead inevitably to 
increased sedimentation and smothering of sea- 
grasses. More bed removal will eventually occur if 
dredging is to be continued to supply the increasing 
demand for sand. 

Small-scale destructive fishing by pull net at 
Pengkalan Nangka, Kelantan, and Paka shoal, 
Terengganu, dislodges the seagrasses and reduces the 
seagrass cover. Harvesting of bivalves, Hiatula solida, 
Meretrix meretrix and Geloina coaxans at Pengkalan 
Nangka, Kelantan, has been shown to cause 
mechanical damage, reduce seagrass cover and retard 
the spread and colonization of seagrasses. Other 
threats include the increasing public use of natural 
seagrass areas, such as for recreational boating, fish- 
ing and swimming in Port Dickson, Negri Sembilan, 
and as avenues for transportation such as in the 
narrow channels in the Paka Lagoon, Terengganu, and 
Sungai Pulai-Merambong-Tanjung Adang_ shoals, 

In Sabah, seagrass and coral reef associated 
ecosystems are areas of gleaning and collection for 
food resources. Uncontrolled collection of flora such as 

Table 14.1 
Estimate of known seagrass areas in Peninsular Malaysia 

State and location Area (ha) 
Pengkalan Nangka Lagoon 40.0 
Kampung Baru Nelayan-Kampung 
Sungai Tanjung 
Pantai Baru Lagoon 
Sungai Kemaman 
Chukai, Kemaman 
Telaga Simpul 
Sungai Paka Lagoon 
Sungai Paka shoal 
River bank of Sungai Paka 
Gong Batu 
Negri Sembilan 
Teluk Kemang 
Tanjung Adang Laut shoal 
Tanjung Adang Darat shoal 
Merambong shoal 
Total estimated area in Peninsular Malaysia 




Case Study 14.3 



The intertidal area and two shoals in the lagoon all 
harbor a mixed Halodule pinifolia and Halophila 
beccarii community. Halodule pinifolia grows in pure 
and extensive subtidal meadows on soft muddy 
substrates at depths of 1.6 to 2.0 m. Halophila 
beccarli grows in shallower parts, at depths of 0.9 to 
1.5 m in monospecific and very dense meadows on 
sandy substrates. The two species are able to 
withstand a wide fluctuation of salinity from 0 to 18 
psu. The meadow is a site for the collection of 
bivalves [e.g. Hiatula solida and Geloina coaxans) 
and artisanal fishing. Digging for bivalves has 
caused a lot of damage to the meadow (see 
photograph). Since 1991 the lagoon has also been 
used for fish cage farming of Lates calcarifer and 
Epinephelus sexfasciatus. Seasonally, from June to 
July, the migrant wader, Egretta garzetta, used the 
shoals as a feeding ground on its migrations until 
two shoals were completely destroyed by sand 
dredging in early 1999. 

Caulerpa spp. and fauna such as sea cucumbers, 
gastropods and bivalves, and illegal fishing with 
explosives are among the major causes of damage to 
coral reefs and associated seagrasses. Such activities 
not only cause loss of flora and fauna but also create an 
imbalance within the ecosystem from which seagrass 
beds are unlikely to recover quickly. 

In the earlier part of this chapter, it was mentioned that 
seagrass beds are the least protected of the three main 
marine ecosystems in Malaysia. It is strongly 
recommended that seagrass beds, especially those 
around offshore islands that have been gazetted as 
marine parks (Pulau Redang; Pulau Perhentian, 
Terengganu; Pulau Tioman, Phang; Pulau Tengah; 
Pulau Besar; Pulau Sibu; Pulau Tinggi, Johore) be given 
protection as marine parks or reserves under the 
Fisheries Act 1985. Under Part IX, Section 41(1) and (2) 
of the Fisheries Act 1985 the Minister of Agriculture 
may order in the Gazette the establishment of any area 
or part of an area in Malaysian fisheries waters as a 
marine park or marine reserve in order to: 
“(a) afford special protection to the aquatic flora 
and fauna of such area or part thereof and to 
protect, preserve and manage the natural 
breeding grounds and habitat of aquatic life, with 

Photo: J.S. Bujang 

Halophila beccarii meadow is a harvesting site for Hiatula solida 
and Geloina coaxans. Digging has caused damage to 
the bed 

particular regard to species of rare or 
endangered flora and fauna; 

(b) allow for the natural regeneration of aquatic 
life in such area or part thereof where such life 
has been depleted; 

{c) promote scientific study and research in 
respect of such area or part thereof; 

({d) preserve and enhance the pristine state and 
productivity of such area or part thereof; and 

({e) regulate recreational and other activities in 
such area or part thereof to avoid irreversible 
damage to its environment.” 

"(2) The limits of any area or part of an area 
established as a marine park or marine reserve 
under subsection (1) may be altered by the 
Minister by order in the Gazette and such order 
may also provide for the area or part of the area 
to cease to be a marine park or marine reserve.” 

The question of affording comprehensive 
protection to marine ecosystems gazetted under the 
present Fisheries Act 1985 has been the subject of 
intense scrutiny by marine scientists, government 
officials and conservationists. The bone of contention 
has been the separation of the land on islands 

gazetted as marine parks and reserves from the 
waters surrounding the islands. Under these circum- 
stances, while the authorities vested with the powers 
to manage and enforce the marine park laws can do so 
at sea, they have no jurisdiction whatsoever over what 
happens on land. 

This could be resolved based on practices 
adopted by Sabah Parks and the present trend of 
promulgating state parks enactment for the protection 
of ecosystems. At present, Sabah Parks has under its 
auspices three marine protected areas: Tunku Abdul 
Rahman Marine Parks, Pulau Tiga Parks and Turtle 
Islands Parks. All harbor seagrasses and were 
gazetted as state parks under the State Parks 
Enactment 1984. Marine areas gazetted as state parks 
in Sabah are afforded more comprehensive protection 
under the enactment than marine parks or reserves in 
Peninsular Malaysia. These parks are protected in their 
entirety without separating the marine and terrestrial 

Several states in Peninsular Malaysia have 
promulgated enactments for the gazettement of state 
parks. Johore has gazetted the National Parks (Johore)} 
Corporation Enactment 1991. Terengganu has a 
Terengganu State Parks Enactment. 

Can the above policies be applied for the 
management of marine protected areas in Peninsular 
Malaysia? The answer lies in encouraging concurrent 
gazettement of marine protected areas under both 
federal and state legislation using the Fisheries Act 
1985 to gazette the protection of the waters 
surrounding the islands as marine parks or reserves, 
and state park enactments to gazette the terrestrial 
component of the marine protected areas as state 


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Support from the United Kingdom Department for International 
Development (DfID) is gratefully acknowledged. 


Japar Sidik Bujang, Department of Biology, Faculty of Science and 
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Selangor Darul Ehsan, Malaysia. Tel: +603 (0)8946 6626. Fax: +603 
(0}8656 7454. E-mail: japar( 

Muta Harah Zakaria, Faculty of Agricultural Sciences and Food, Universiti 
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of Fisheries Malaysia, Ministry of Agriculture Malaysia, Kuala 

15 The seagrasses of 

The western Pacific islands 


countries and island states of Micronesia, 

Melanesia and Polynesia. These countries are 
located in the tropical Pacific Ocean; almost all the 
islands are in a zone spanning the equator from the 
Tropic of Cancer in the north to the Tropic of Capricorn 
in the south. 

Most islands, with the exception of Papua New 
Guinea and Fiji, are small by continental standards 
and are separated by expanses of deep ocean waters. 
It is no easy task estimating even the number of 
islands in the western Pacific region. For example 
there are in excess of 2000 islands in Micronesia 
alone, some of which may not be permanent and can 
be swamped by high tides. There are two main types 
of islands - the high islands such as Fiji, Papua New 
Guinea and most of the Solomon Islands, and the low 
islands and coral reef atolls such as Majuro and 
Kiribati. In the Pacific, as in the rest of the world, most 
of the cities and towns are located in the coastal 
region. Only in Papua New Guinea are there large 
towns located away from the coast. There has been a 
marked change away from mostly subsistence living. 
As a consequence Pacific islanders are no longer 
totally rural, and urban growth is outstripping total 
growth. Human populations are increasing throughout 
the region and can be as high as 23 000 people per km* 
(e.g. Marshall Islands]". 

Most countries in the Pacific list human waste 
disposal as a significant issue and this is likely to 
affect seagrass meadows. Only larger towns have 
sewage systems, but most of the effluent discharges 
into the sea". Along with septic systems and village 
latrines, the eventual nutrient loads of sewage 
systems to inshore and reef platform seagrasses may 
be significant. Custom ownership of land [inherited 
ownership of land and nearshore regions by 
indigenous villages or families) gives the owners the 
right to do as they wish with the land even if that leads 

T=: western Pacific island region includes the 

R. Coles 

L. McKenzie 
S. Campbell 
M. Fortes 

F. Short 

to environmental damage. While these issues are 
recognized and are being addressed by planning 
legislation, enforcement is difficult or impossible in 
many of the islands. This dilemma of land tenure may 
be an obstacle to the environment planning needed to 
ensure a sustainable habitat for seagrass. 

There are 24 species of seagrasses, including 
Ruppia”, found throughout the tropical Indo-Pacific”. 
Our best estimate is that 13 of these are found in the 
western Pacific islands. These include the genera of 
Cymodocea, Enhalus, Halodule, Halophila, Syringo- 
dium, Thalassia and Thalassodendron. \t is possible 
that new species remain to be described from the 
western Pacific, as collections from this region are 
relatively few. Seagrass species distribution across the 
western Pacific is believed to be influenced by the 
equatorial counter-current in the northern hemi- 
sphere and the equatorial current in the southern 
hemisphere“, with the number of species declining 
with easterly distance. The reduced bottom area 
available and the effect of past changes in sea level 
would also reduce species numbers along an easterly 
gradient’. The numbers are greatest near the biggest 
land mass, with 13 species in Papua New Guinea”, and 
least in the easternmost islands; only one species is 
known from Tahiti”. 

Seagrasses across the region are also often 
closely linked, with complex interactions, to mangrove 
communities and coral reef systems. Dense seagrass 
communities of Enhalus and Cymodocea are often 
present on the intertidal banks adjacent to mangroves 
and fringing reefs. 


Western Pacific seagrass communities grow on 
fringing reefs, in protected bays and on the protected 
side of barrier reefs and islands. Habitats most suited 
to tropical seagrasses are reef platforms and lagoons 
with mainly fine sand or muddy sediments enclosed 



by outer coral reefs. These habitats are influenced by 
pulses of sediment-laden, nutrient-rich freshwater, 
resulting from seasonally high summer rainfall. 
Cyclones and severe storms or wind waves also 
influence seagrass distribution to varying degrees. On 
reef platforms and in lagoons the presence of water 
pooling at low tide prevents drying out and enables 
seagrass to survive tropical summer temperatures. 

Enhalus acoroides is the only species that 
releases pollen to the surface of the water when 
reproducing sexually. This feature restricts its 
distribution to intertidal and shallow subtidal areas. It 
is a slow-growing, persistent species with a poor 
resistance to perturbation”, suggesting that areas 
where it is found are quite stable over time. Cymodocea 
is an intermediate genus that can survive a moderate 
level of disturbance, while Halophila and Halodule are 
described as being ephemeral genera with rapid 
turnover and high seed set, well adapted to high levels 
of disturbance”. 

Thalassia hemprichii is the dominant seagrass 
found throughout Micronesia and Melanesia, although 
it is absent from Polynesia and Fiji. Thalassia 
hemprichii is often associated with coral reefs and is 
common on reef platforms where it may form dense 
meadows. It is able to grow on hard coral substrates 
with little sediment cover. It can also be found 
colonizing muddy substrates, particularly where water 
pools at low tide. In the Indo-Pacific region, Thalassia 
hemprichii is commonly the climax seagrass species. 
Species of Halodule, Cymodocea and Syringodium may 
at times also be found in dense meadows associated 
with reefs and on reef platforms. Enhalus acoroides 
and Cymodocea rotundata are also widespread 
throughout the region but absent from Polynesia and 
Fiji. Halodule uninervis is abundant throughout 
Melanesia and Polynesia, but is only found in Guam and 
Palau in Micronesia. Both Cymodocea serrulata and 
Cymodocea rotundata were recorded in intertidal 
regions of Micronesia” and in Papua New Guinea, 
eastern Micronesia and Vanuatu”. 

Syringodium isoetifolium has only been recorded 
in the most westerly islands of Micronesia (e.g. Palau 
and Yap], in Tonga and Samoa in Polynesia, in Papua 
New Guinea, and in Vanuatu and Fiji in Melanesia. In Fiji 
Syringodium isoetifolium occurs as a widespread and 
dominant seagrass species. 

Halophila species are widespread through the 
Pacific islands with the exception of the eastern 
Micronesia islands. In the western islands of the west- 
ern Pacific, Halophila ovalis is found in intertidal habitat 
mixed with larger seagrass species like Enhalus 
acoroides in Palau or Thalassia hemprichii in Yap. 
Halophila ovalis is also commonly found in deep water 
at the offshore edge of mixed seagrass meadows. The 

only Halophila species present in Fiji is the subspecies 
Halophila ovalis bullosa identified by den Hartog”. 

Thalassodendron ciliatum has been recorded 
from Palau, Papua New Guinea and Vanuatu'™”. It is 
unusual in being restricted almost exclusively to rocky 
or reef substrates. It is often found on reef edges 
exposed to wave action, protected from damage by its 
flexible woody stem and strong root system. It can be 
difficult to locate because of its exposed reef edge habit 
and is uncommon in records from most Pacific island 

Generally low nutrient availability’ is a likely 
determining factor in seagrass extent on reef habitats 
across the western Pacific islands. Seagrasses 
frequently grow more abundantly on intertidal reef 
platforms and mud flats adjacent to populated areas 
where they can utilize the available nutrients. Seagrass 
communities in the western Pacific islands must 
tolerate fluctuating and extreme temperatures, fluc- 
tuating salinity during rainfall seasons, and exposure to 
storm-driven waves and erosion. Often the sediments 
are unstable and their depth on the reef platforms can 
be very shallow, restricting seagrass growth and 

Most tropical species in the western Pacific are 
found in waters less than 10 m deep. There is a complex 
depth range for seagrasses as the availability of bottom 
substrate and shelter for seagrass growth is controlled 
by the topography of coral reef communities which often 
protect the seagrass habitats from wave action. The 
location of the seaward edge may be determined by the 
depth or location at which coral cover becomes consis- 
tent or by the edge of a platform that drops rapidly into 
deeper water. This distribution and the topographic 
features controlling it differ from many temperate 
regions where availability of light for photosynthesis 
controls the depth penetration of seagrasses. 

Exposure at low tide, wave action and low salinity 
from freshwater inflow determine seagrass species 
survival at the shallow edge. Seagrasses survive in the 
intertidal zone especially at sites sheltered from wave 
action or where there is entrapment of water at low 
tide (e.g. reef platforms and tide pools) protecting the 
seagrasses from exposure (to excessive heat or drying) 
at low tide. At the deeper edge, light, wave action and 
the availability of suitable bottom substrate limit 

The stresses and limitations to seagrasses in the 
tropics are generally different from those in temperate 
or subarctic regions. They include thermal impacts 
from high water temperatures; desiccation from 
overexposure to warm air; osmotic impacts from 
hypersalinity due to evaporation or hyposalinity from 
wet season rain; radiation impacts from high irradiance 
and UV exposure. Both Halophila ovalis and Thalassia 


« Pikelot 

Woleai « 

Eaunpik * 




Inan Jaya 
(West Papua) 



| at 2 


ee Culfof Papua 
Port Morea 





Santa Cruz Is. 




600 800 1000 Kilometers 

170° E 
Maps 15.1 and 15.2 
Western Pacific islands (west) (top) and Western Pacific islands (east) 

hemprichii were found in intertidal regions in Yap, 
Micronesia’, where tolerance to 40°C temperatures 
and low salinity allow these species to colonize. Other 
species present in Yap, Syringodium isoetifolium and 
Cymodocea serrulata, were restricted to deeper water 
by these conditions. 

Reef platform seagrass meadows support a wide 
range of mollusks, fish, holothurians and decapods. 
The available literature does not focus on the ecological 
role of seagrasses and information on complex 



The western Pacific islands 


a (Truk) _Pohnpei 

* Mwokil 

* Satawan 
* Kosrae 


0 100 200300400500 Kilometers 0 
mE a ha 

“\s Kavieng 



Milne Bay 

150° E 160° ES 



Nukubuco Reef 


community interactions presented for reef flat species 
may not necessarily refer to areas with seagrass. 
Munro’ lists 75 species of mollusks collected by 
subsistence gleaners in the Solomon Islands, Papua 
New Guinea and Fiji from mangroves, reefs, seagrass 
meadows and sand flats. Other mollusks such as the 
trochus shell {Trochus niloticus) found in seagrass 
meadows are collected as a source of cash income. 
Similarly the holothurians have been a valuable source 
of cash income, although now heavily overfished'’. We 




have found lower value species such as Holothuria atra 
to be still common in seagrass meadows in parts of 

Pyle" lists at least 3 392 reef and shore fish from 
the Pacific islands but it is not possible to distinguish 
which species are from seagrass meadows. Klumpp et 
al.'"' refer to 154 species of tropical invertebrates and 
fish that feed directly on seagrasses and Coles et al.'"” 
list and classify 134 taxa of fish and 20 shrimp species 
found in tropical Australian seagrass meadows giving 
some indication of the likely use of tropical Pacific 
seagrass meadows. 

Case Study 15.1 

The Federated States of Micronesia is made up of 

~ four states: Kosrae, Pohnpei, Chuuk and Yap. Kosrae 
is the easternmost state and consists of two islands: 
a large mountainous island approximately 20 km 
long and 12 km wide, and a smaller 70 ha island, 
Lelu, approximately 1 km off the northeast coast of 

A detailed assessment of Kosrae reef 
environments in 1989 (carried out by the US Army 
Corps of Engineers, Coastal Engineering Research 
Center] mapped approximately 3.5 km? of seagrass 
meadows around the islands. Seagrass meadows 
were restricted to reef tops. Large dense meadows 
were mapped adjacent to Okat and Lelu Harbours. 



Lelu Harbour ca 1900. 

Seagrasses are also food for the green turtle 
(Chelonia mydas), found throughout the Pacific island 
region, and for the dugong {Dugong dugon), found in 
small numbers feeding on seagrasses in the western 
islands - Palau, Vanuatu and the Solomon Islands. 


The major changes in Pacific island seagrass meadows 
have occurred mostly in the post-Second World War 
period and are related to transport infrastructure, 
tourist development and population growth. Some 
islands have seagrass maps available but most do not 

Species of seagrass found were Enhalus acoroides, 
Thalassia hemprichii and Cymodocea rotundata. 

Over the last three to four decades there has 
been considerable coastal construction activity on 
the islands to build modern transportation facilities, 
and the seagrass meadows and reef flats at those 
locations have been severely impacted. Two aircraft 
runways and associated causeways have been 
constructed on the only available flat area on the 
island — the reef flat. 

The first runway was constructed on the 
shallow flat between Kosrae and Lelu Islands in 
the late 1960s and early 1970s. Maragos'”! 
reported that the causeway connecting to this 
runway construction had adverse effects on Lelu 
Harbour. The original causeway blocks the water 
circulation and fish runs into inner Lelu Harbour, 




Kilometers = 
Lelu Harbour 1975. 

have information recorded with the precision required 
to identify any historical change. It is likely that some 
information exists in unpublished reports and 
environmental assessments for areas subject to 
development but, where it exists, this information is not 
readily available. 

Human population growth and the need to provide 
tourist accommodation have led to filling in some 
coastal areas to provide new land. Certainly port 
developments and small boat marinas have been 
constructed in locations without taking the presence of 
seagrass meadows into account". Nutrient inputs 

leading to a decline in seagrasses and fish catches 
and increased pollution problems. Fill for the 
runway expansion further reduced water circu- 
lation, fish yields, water quality and seagrasses in 
the harbor. 

In the mid-1980s, a new airport and dock were 
constructed in Okat Harbour on the north of Kosrae 
Island. Construction buried a large area of the 
offshore reef flat seagrass meadows (see sketch 
maps below}. Also, during dredging activities, the 
rate of slurry discharged into a retention basin 
exceeded the basin’s capacity, causing the slurry to 
overflow and burying an adjacent 10 ha of seagrass 
and coral habitat under 0.25-0.5 m of fine mud. 

The construction also changed the water 
circulation, and the strong currents caused 
shoreline erosion. These impacts are reported to 


es, Harbour” ~_- yy 

Okat Harbour and Reef 1978. 

The western Pacific islands 

from expanding coastal urban development may have 
increased the biomass of seagrass on nearby reef plat- 
forms. In general, though, there is not sufficient histor- 
ical written information from which to draw direct 
conclusions on historic trends. Munro’ does report 
that 2000-year-old mollusk shell middens in Papua 
New Guinea have essentially the same species 
composition as present-day harvests, suggesting 
indirectly that the habitats, including seagrass habitats 
and their faunal communities, are stable and any 
changes occurring are either short term or the result of 
localized impacts. 

have reduced Okat reef’s fish harvest to half that of 
pre-construction levels. 

The unintended environmental effects of these 
constructions are continuing with shore erosion and 
restoration by revetment still occurring at Lelu 
Harbour and adjacent to villages near the new 
airport. While it is easy to criticize a decision to build 
infrastructure on top of coral reef platforms, it is 
hard to suggest a feasible land-based solution on 
such a mountainous island. Flat areas available are 
either inhabited or mangrove covered. It would be 
hoped that if these projects or similar were under- 
taken today, better environment management sys- 
tems in place would at least reduce the unintended 
effects and slurry overflow that occurred. 

Source: Maragos'"”!. 

‘ — ! 

j a. a 
/ , Ss Si 
f A f i F 


Okat Harbour and Reef 1988. 



Photo: FT. Short 


Banded sea snake swimming over Syringodium isoetifolium and 
Halodule uninervis meadow, Nukubuco Reef, Fiji 


In the western Pacific, local coastal developments for 
tourism or transport infrastructure are the major cause 
of seagrass loss. In Kosrae and other members of the 
Federated States of Micronesia the development of local 
airports has contributed to a loss of seagrass on reef 
platforms. The Kosrae airport, for instance, is placed on 
landfill covering a reef platform and seagrasses’. In 
Palau, the building of causeways without sufficient 
consideration of the need for culverts to maintain water 
flow has caused localized seagrass loss. In Fiji, 
eutrophication and coastal development are the primary 
causes of seagrass loss. Little information is available 
on the loss of seagrass habitats in Papua New Guinea, 
but away from major population centers losses are 
likely to be small and again associated with transport 

Maragos'”'details the loss of mainly coral reef flat 
habitat, but including seagrasses and mangroves, in 
the Federated States of Micronesia from construction 
activities associated with plantations, transportation, 
military activity, urban development, aquaculture 
development and resort development. Coastal road 
construction around the islands of Pohnpei and Kosrae 
resulted in the dredging of many hectares of seagrass 
and mangrove habitat. 

Losses of seagrasses such as these are likely to 
be widespread across the Pacific islands as there has 
been little attention paid to protecting seagrasses. 
Modern mapping and monitoring techniques should in 
the near future enable some baseline estimation of the 
total areas of the seagrass resources of the region. 


Species lists are available for the western Pacific 
region” but they are not available for many of the 
individual islands. Coles and Kuo'” list seagrass 
species from 26 islands [including the Hawaiian Islands 
and Papua New Guinea) based on published records, 
examination of herbarium specimens and/or site visits 
by the authors. Species numbers ranged from 11 on 
Vanuatu to a single species in the Marshall Islands. The 
numbers in Coles and Kuo'” are conservative in some 
cases because they do not include unpublished reports 
or records. Maps of seagrass are not readily available 
or are of relatively poor quality and/or reliability. Some 
estimation might be possible based on the high 
likelihood of almost all shallow [<2 m below mean sea 
level) reef flats having at least a sparse seagrass cover, 
but no numerical estimation of seagrass cover in the 
western Pacific has been made to date. 

Geographic information system (GIS) initiatives in 
the Federated States of Micronesia by the South Pacific 
Regional Environment Program should improve map 
coverage. Simple GIS maps are already available for 
Kosrae although they are based on earlier aerial 
mapping and would not be precise enough for detailed 
management purposes. Project assistance to update 
and validate these maps would accelerate the process 
of providing a publicly available set of maps for these 
islands. Partial maps are available for other western 
Pacific islands although their validity is uncertain and 
likely to be variable. 

CSIRO (Australia’s Commonwealth Scientific and 
Industrial Research Organisation) has recently surveyed 
Milne Bay Province in Papua New Guinea. Seagrass was 
seen at 103 locations out of a total of 1126. Seagrass 
was found at several areas throughout the province, 
mostly on shallow areas adjacent to the larger islands 
such as the Trobriand, Woodlark and Sudest Islands. 
Cover was up to 95 percent in these areas. The 
dominant species were Thalassia hemprichii, Enhalus 
acoroides and Halophila ovalis with some Cymodocea 
serrulata, Halodule uninervis and Syringodium 
isoetifolium™”. To the best of our knowledge no other 
broadscale surveys have been conducted for Papua New 
Guinea outside individual published site descriptions. 


Traditional uses of seagrass by communities in the 
western Pacific include manufacture of baskets; 
burning for salt, soda or warmth; bedding; roof 
thatch; upholstery and packing material; fertilizer; 
insulation for sound and temperature; fiber 
substitutes; piles to build dikes; and for cigars and 
children’s toys’. Enhalus acoroides fiber is also 
reported to be used on Yap, Micronesia, in the 
construction of nets”. Enhalus acoroides fruit is 


Regional map: The Pacific 

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Recreational fisher standing in a seagrass bed, Bali, Indonesia Food [bivalves] collected from seagrass beds, Mozambique 

Beach seine is 
Ph uppines WW Cd 

Harvesting abalone from 

Phyllospadix Harvesting Zostera marina for 

spp. ca 1914, Pacific coast of USA transplanting, Maine, USA = 

Snorkeler over a long-bladed Zostera marina bed in New Hampshire, USA 

Trap fisherman Anibal Amade in 

A fisher family on Quirimba Island, Mozambique with the 
catch from a trap fishing trip in the seagrass beds 

eaten in some Australian traditional communities and 
in some parts of the western Pacific. 

Coastal development, dredging and marina 
developments are generic threats to seagrass in the 
tropical tourist regions but areas lost are generally 
small. Causeway development in Palau'’” without 
culverts to allow water flow has led to large seagrass 
losses as water stagnates and sediment builds up. 
Coastal agriculture may add to sediment loads in 
catchments in Papua New Guinea and Fiji. Shipping 
management influences seagrass survival adjacent to 
shipping lanes and port locations. 

Climate change and associated increase in storm 
activity, water temperature and/or sea-level rise have 
the potential to damage seagrasses in the region and to 
influence their distribution causing widespread loss. 
Reef platform seagrasses are already exposed to water 
temperatures at low tide greater than 40°C and an in- 
crease in temperature may restrict the growth of the 
inner shallow edge of reef platform seagrass. Sea-level 
rise and associated increased storm activity could lead 
to large seagrass losses through increased water move- 
ment over seagrass beds and erosion of sediments. It is 
possible that with a rise in sea level areas that are now 
seagrass habitat may be colonized by coral. 


Many western Pacific island communities have 
complex and at times unwritten approaches to land 
ownership, custom rights and coastal sea rights. These 
are partially overlaid by arrangements put in place by 
colonizing powers during and after the Second World 
War, leaving the nature and strength of protective 
arrangements open for debate’. In implementing any 
protective arrangements for seagrasses the challenge 
will be to develop an approach that will suit all parties 
and that will respect traditional ownership rights. This 
must also be achieved in an area where enforcement, at 
least in the sense it is used in North America and 
Europe, is absent or ineffective and more of a 
consensus approach will be required. 

We are not able to find any legislation or 
protective reserve systems that are specifically 
designed to protect seagrasses. Existing reserves, 
however, often include seagrasses and legislation to 
protect mangroves or marine animals such as trochus 
shell may indirectly protect seagrass meadows. 

The South Pacific Regional Environment 
Programme Action Strategy for Nature Conservation in 
the Pacific Islands region lists 232 established protected 
areas and community-based conservation areas in the 
Pacific islands. Some, such as the Okat trochus sanc- 
tuary in Kosrae and the Ngerukewid Islands reserve in 
Palau, provide some level of indirect protection. 

Under the Law of the Sea Treaty, coastal nations 

The western Pacific islands 

are bound to protect the marine environments under 
their control. There are some 13 other international 
conventions and treaties which could have some 
bearing on seagrass management although in reality it 
is hard to measure any quantifiable outcomes that 
protect seagrasses whether the programs are ratified 
or not. 

At a regional level, laws relating to impact 
assessment and town planning have an indirect ability 
to protect seagrass from loss. In Fiji the Town Planning 
Act deals with environmental impact assessments. 

Halophila ovalis, a species commonly found in the western Pacific 

Land below high water is administered by the Ministry 
for Land and Mineral Resources through the 
Department of Lands and Surveys. If a mangrove area 
{and presumably also seagrasses] is be reclaimed, the 
application is referred to the Department of Town and 
Country Planning for comment, recommendation and 
suggested conditions. It may also be referred to the 
Department of Fisheries and the Native Fisheries 
Commission for arbitration of compensation”. 

In Papua New Guinea the Environmental Planning 
Act requires a plan for a development project to be 
submitted to the Department of Environment and 
Conservation for approval”. Palau’s conservation laws 
are cited in the Palau National Code Annotated and are 
described by the Palau Conservation Society” in an 
easy-to-understand form. 

Two trends are emerging from the Pacific islands. 
One is the recognition of the need for sanctuaries and 
protected areas and the other the concept of traditional 
or community management of these areas’. The role 
being played by non-governmental organizations, 
focused on conservation and environment protection 
integrated with traditional leadership and government 

Photo: J.S. Bujang 



Case Study 15.2 

SeagrassNet is a global monitoring program that 
investigates and documents the status of seagrass 
resources worldwide and the threats to this 
important ecosystem. Seagrasses, which grow at 
the interface of the land margin and the world’s 
oceans, are threatened by numerous anthropogenic 
impacts. There is a lack of information on the status 
and health of seagrasses, particularly in the less 
economically developed countries. SeagrassNet's 
efforts to monitor known seagrass areas and to map 
and record uncharted seagrasses in the western 
Pacific are important first steps in understanding 
and maintaining seagrass resources worldwide. 
Synchronous and repeated global sampling of 
selected environment and plant parameters is 
critical to comprehending seagrass status and 
trends; monitoring these ecosystems will reveal 
both human impacts and natural fluctuations in 
coastal environments throughout the world. 

SeagrassNet was developed with two com- 
ponents. Research-oriented monitoring methods 
are based on recently compiled seagrass research 
techniques for global application”, while 
community-based seagrass monitoring effort is 
modeled after Seagrass-Watch” - an Australian 
seagrass community [citizen] monitoring program 
that is conducted simultaneously with research- 
based monitoring so that comparisons of the 
resulting data are possible. 

An important part of the communication 
strategy for SeagrassNet is an interactive system 
established on a website, with data entry, archiving, 
display and retrieval of seagrass habitat-monitoring 
data, ranging from plant species distribution to 
animal abundance and records of localized die-offs. 
SeagrassNet both acquires and provides monitoring 
data in a format for information sharing. 


Before the program can become fully established, a 
pilot study is being conducted to develop a globally 
applicable seagrass monitoring protocol, to 
compare science-based with community-based 
monitoring efforts and to test the feasibility and 
usefulness of this publicly available database 
retrieval network. The western Pacific was chosen 
for the pilot because it has extensive and diverse 
seagrass habitats and a myriad of coastal issues 
with the potential to threaten seagrass growth and 

survival. Challenges to seagrasses in the western 
Pacific are numerous and, similar to those in most 
parts of the world, range from human population 
increase, fisheries practices, pollution and onshore 
development to global climate change and sea-level 
rise. The combination of these factors and the 
remoteness of many locations provide a complex set 
of circumstances that challenges our scientific 
ability to monitor seagrass habitat and to test the 
diversity of habitat impacts. The western Pacific 
region includes underdeveloped countries that have 
extensive seagrass habitat linked to important 
economic activities such as fishing, tourism and 
sports diving. The constraints of resources and the 
relatively small number of seagrass scientists in the 
western Pacific have to date precluded extensive 
surveys and monitoring of the kind common in 
Europe and parts of the US and Australian coast. 

With funding assistance from the David and 
Lucile Packard Foundation, eight locations, five of 
which are western Pacific islands, were identified as 
suitable. In mid-2001, long-term monitoring sites 
were established in Kosrae, Pohnpei, Palau, 
Kavieng (Papua New Guinea) and Fiji. Scientists 
were identified at each location to take part in the 
direct field monitoring aspect of the research. 
Quarterly monitoring is now being conducted at 
designated sites in each country. Sites chosen were 
representative of the dominant seagrass habitat 
existing in each location. 

In Kosrae, a monitoring site was established in 
a trochus sanctuary adjacent to Okat Harbour on the 
north of Kosrae Island. The site is on an intertidal 
fringing reef borded by mangroves landward and the 
reef edge seaward. Seagrass meadows cover much 
of the fringing reef where coral is absent. It is 
predominately an Enhalus acoroides meadow 
inshore, which changes to a meadow dominated by 
Thalassia hemprichii and Cymodocea rotundata 
seaward. The Fisheries Development Division is 
monitoring the site with some assistance from the 
Kosrae Development Review Commission. 

On the island of Pohnpei, the largest island 
and location of the capital of the Federal States of 
Micronesia, a monitoring site was established on a 
relatively remote fringing reef at the southernmost 
point of the main island in an area free from physical 
disturbance by human activity. The site is on a reef 
flat where water pools at low tide, and is similar to 
the site monitored on Kosrae, including the species 
Enhalus acoroides and Thalassia hemprichil. 
Scientists from the College of Micronesia are 
monitoring the site. 

In the Republic of Palau a monitoring site was 
established on a fringing reef at the edge of the 
shipping channel on Koror. The meadow extends 
across the intertidal reef flat from the mangrove- 
lined shore to the reef crest. Inshore, the meadow is 
predominately Enhalus acoroides, becoming inter- 
spersed with Thalassia hemprichii, which increases 
in presence along with Halodule uninervis and 
Halophila ovalis seaward. The site is adjacent to 
coastal development and receives stormwater and 
agricultural runoff. Scientists of the Palau Inter- 
national Coral Reef Centre and Coral Reef Research 
Foundation are monitoring this site. 

In Papua New Guinea, seagrass monitoring 
was conducted near Kavieng in New Ireland, an 
island province in the northeast. With the permission 
of the village leader a monitoring site was estab- 
lished on the fringing reef flat of a small island, 
Nusa Lik. The site is intertidal with a mixture of 
Halodule uninervis, Enhalus acoroides, Thalassia 
hemprichii, Cymodocea serrulata and Halophila 
ovalis. The outer edge of the seagrass was deter- 
mined by the edge of the coral reef. Staff attached to 
the Fisheries Research Laboratory and local fish- 
eries college are monitoring the site. 

Fiji has environmental issues similar to the 
other western Pacific island countries, such as 
deforestation, soil erosion and sewage effluent. A 
monitoring site was established on Nukubuco Reef 
in Laucala Bay. This monitoring site is different from 
sites at other localities, as it is on a barrier reef. No 
suitable fringing reef sites similar to other 
participating countries could be found. The site was 
chosen because the seagrass distribution and 
abundance of Nukubuco Reef have been mapped as 
part of a University of the South Pacific postgraduate 
project and the site was easily accessible from Suva. 
The monitoring site is adjacent to a sand cay at the 
northwestern edge of the reef. It is an intertidal site 
with a mixture of Halodule uninervis, Halodule 
pinifolia and Halophila ovalis subsp. bullosa close to 
the cay, becoming a monospecific Syringodium 
isoetifolium meadow seaward. The outer edge of the 
meadow was determined by the edge of the channel. 
Scientists from the University of the South Pacific 
are monitoring the site. 

The community-based seagrass monitoring 
program that forms the second stage of the project 
was initiated in the western Pacific islands in April 
2002 in New Ireland, Papua New Guinea. In June and 
July 2002 local citizens also began monitoring sites in 
Kosrae, Palau and Fiji. Community participants were 
mostly school students and local villagers. 

The western Pacific islands 

Community monitoring sites were established on 
intertidal fringing reefs and local scientists, 
government and non-governmental organizations are 
providing support. The program is using the existing 
Australian Seagrass-Watch program 
data entry systems. 

"5! brotocols and 

Thalassia hemprichii and Cymodocea rotundata meadow on 
intertidal fringing reef, Kosrae, Federated States of Micronesia. 


Preliminary results from the scientific monitoring 
indicate that the sampling protocols appear suitable, 
although adjustments and refinements may occur 
from time to time as the program develops. Data 
entry via the website {] was 
successful, although access to the Internet is limited 
in some countries. Quality control and data 
validation are being completed at the University of 
New Hampshire's Jackson Estuarine Laboratory. 
Photographic collections are being cataloged and 
archived by the Queensland Department of Primary 
Industry Marine Plant Ecology Group. Herbarium 
samples were also verified at the University of New 
Hampshire and sent to the International Seagrass 
Herbarium at the Smithsonian Institution, 
Washington, DC, USA. 

The initial success of the pilot study has 
encouraged scientists and coastal resource 
managers in Africa, South America, Asia, Europe, 
Australia and North America to participate. The goal 
is to expand SeagrassNet to other areas of the globe 
and, ultimately, to establish a network of monitoring 
sites linked through the Internet by an interactive 
database. The ultimate aim is to preserve the 
seagrass ecosystem by increasing scientific 
knowledge and public awareness of this threatened 
coastal resource. 

Photo: L. McKenzie, DPI 




agencies, suggests that conservation measures and 
the acceptance of enforcement will continue to 

There is a growing understanding that community 
types such as seagrasses are vital to the health of the 
reef environment and that they are threatened by climate 
change as well as direct human impacts. There is clearly 
a need in the Pacific island nations to quantify the risks 
to seagrass of present management practices and to 
quantify the extent and value of seagrass protection 
afforded by the present reserves and legislative 


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Miguel Fortes, Marine Science Institute CS, University of the Philippines, 
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Fred Short, Department of Natural Resources, University of New 
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Durham, NH 03824, United States. 

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16 The seagrasses of 


[though seagrasses cover at least 30000 km? 
Aevossnas the Indonesian Archipelago, from 
Pulau Weh in Aceh to Merauke, Papua, they have 
only been studied in relatively small areas and 
information is therefore rather limited. Nonetheless an 
encouraging and increased understanding of the 
importance, ecology and biology of Indonesian 
seagrasses has developed in recent years". Vast areas 
of the archipelago [e.g. the north coast of Papua, the 
southwest coast of Indonesia, the south and west 
coasts of Kalimantan) are yet to be studied, however. 
The diversity of marine habitats in Indonesia is 
among the highest in the world and Indonesian sea- 
grass diversity is comparable to other countries in the 
region. Seven genera and 12 species of seagrasses 
currently occur in Indonesian waters”. Two species, 
Halophila spinulosa and Halophila decipiens, have 
been recorded in just a few locations: Halophila 
spinulosa in Sorong [Papua], Lombok, East Java, Sunda 
Strait and Riau, and Halophila decipiens in Aru, Kotania 
Bay, Lembata, Sumbawa and Jakarta Bay. Two further 
species, Halophila beccarii and Ruppia maritima, are 
known only through specimens at the Bogor Herbarium 
and have not recently been found in the field. 
Indonesian seagrasses either form dense 
monospecific meadows or mixed stands of up to eight 
species. Thalassia hemprichii, Enhalus acoroides, 
Halophila ovalis, Halodule uninervis, Cymodocea serru- 
lata and Thalassodendron ciliatum usually grow in 
monospecific beds’, and muddy substrates on the 
seaward edges of mangroves often have meadows of 
high biomass. Mixed-species meadows occur in the 
lower intertidal and shallow subtidal zones, growing best 
in well-sheltered, sandy (not muddy], stable and low- 
relief sediments. These beds are typically dominated by 
pioneer species such as Halophila ovalis, Cymodocea 
rotundata and Halodule pinifolia. Thalassodendron 
ciliatum dominates the lower subtidal zone - this 
species can grow in silt as well as in medium-to-coarse 


T.E. Kuriandewa 
W. Kiswara 

M. Hutomo 

S. Soemodihardjo 

sand and coral rubble. High bioturbation by, for example, 
burrowing shrimps tends to decrease seagrass density 
and favor the pioneer species. Seagrasses growing in 
terrigenous sediment are more influenced by the 
turbidity, seasonality, fluctuating nutrient and salinity 
concentrations, and subsequent light limitation, of land 
runoff than those in reef-derived carbonate sediments 
with less variable seasonal dynamics. 

Monospecific beds of Thalassia hemprichii are 
the most widespread throughout Indonesia and occur 
over a large vertical range from the intertidal zone 
down to the lower subtidal zone”. Halophila ovalis also 
has a wide vertical range, from the intertidal zone down 
to more than 20 m depth, and grows especially well on 
disturbed sediments such as the mounds of burrowing 
invertebrates. Enhalus acoroides, too, grows in a 
variety of different sediment types, from silt to coarse 
sand, in subtidal areas or localities with heavy 
bioturbation. Halodule uninervis is a pioneer species, 
usually forming monospecific beds on the inner reef 
flat or on steep sediment slopes in both the intertidal 
and subtidal zones. 

The majority of detritus produced by Indonesian 
seagrasses is believed to settle within the beds, with an 
estimate of only 10 percent exported to other 
ecosystems’. Most of the nutrients lost by leaf 
fragmentation through decomposition or harvesting by 
alpheid shrimps are translocated to the sediment and 
about 80 percent of the nitrogen content is denitrified 
there”. This retention of nutrients within the beds may 
explain why seagrass beds in Indonesia maintain a high 
level of productivity despite low nutrient availability. 
Detailed studies of the nutrient concentrations at 
six different locations in the Spermonde Archipelago of 
South Sulawesi have indicated that there are structural 
and functional differences between coastal beds 
growing on the sand and mud deposited by rivers, and 

eae 172 


Table 16.1 
Average biomass of seagrasses (g dry weight/m’) at various locations throughout Indonesia 

Sunda Banten 
Strait Bay 

1976 353-560 
Cymodocea rotundata 37-106 139 
Cymodocea serrulata 48-104 15-35 
Halodule pinifolia = cs 
Halodule uninervis 10-36 6-80 
Halophila ovalis 2-4 8 
Syringodium isoetifolium 74 102-372 
Thalassia hemprichii 87-193 120-257 
Thalassodendron ciliatum - - 


Enhalus acoroides 

Source: Kiswara"” 

Table 16.2 

Jakarta Flores Lombok 
Bay Sea 

250-663 155-546 393-2 479 

18-23 34-113 39-243 

45-174 111 

29-126 47 

13-516 29-128 

1-3 4-46 

33-127 85-262 

115-322 53-263 

231-444 - 

Average density of seagrasses (shoots/m’] at various locations throughout the Indonesian Archipelago 

Sunda Banten 
Strait Bay 

Enhalus acoroides 160 40-80 
Cymodocea rotundata 38-756 690 
Cymodocea serrulata 48-1 120 60-190 
Halodule pinifolia = - 
Halodule uninervis 10-335 40-1 160 
Halophila ovalis 15-240 820 
Syringodium isoetifolium 630 124-3 920 
Thalassia hemprichii 30-315 220-464 
Thalassodendron ciliatum = - 


therefore of terrestrial origin, and those growing 
offshore on sediments derived from coral reefs. 
Concentrations of dissolved reactive phosphate, 
ammonium and nitrate+nitrite were low [<2 uM] in the 
water column at all sites, often below detectable limits, 
but considerably higher in sediment porewater™. 
Porewater phosphate concentrations (3-13 uM) were 
comparable between the two sediment types, but 
exchangeable phosphorus contents were two to five 
times higher in carbonate sediment [(18.2-23.6 mg 
phosphorus/100 g versus 4.4-10.9 mg phosphorus/100 
g) than in terrigenous sediments. Carbonate sediments 
were extremely low in organic matter compared with 
terrigenous sediments. 

The more vigorous growth of coastal seagrasses 
is attributed to a higher level of nutrients in the 
sediment than offshore. Leaf size of Enhalus acoroides 
is significantly larger in coastal than offshore beds”, 
biomass and shoot densities are higher and epiphyte 

Jakarta Flores 
Bay Sea 
36-96 60-146 50-90 

26-1 136 220-1 800 253-1 400 
1056 115-1 600 362 

- 430-2 260 7120 

604 360-5 600 80-160 
18-115 100-2 160 400-1 855 
144-536 360-3 740 1 160-2 520 
68-560 160-1 820 200-865 
- 400-840 - 


cover lower, factors attributed to the less severe 
environmental fluctuations of offshore beds”. 


The below-ground rhizome biomass of Enhalus 
acoroides is six to ten times larger than that of above- 
ground biomass". Cymodocea rotundata, Cymodocea 
serrulata and Halodule uninervis have higher below- 
ground biomass when growing in established mixed 
vegetation beds than in monospecific pioneer beds“. In 
general, species characteristic of climax Indonesian 
seagrass meadows (Thalassia hemprichii, Enhalus 
acoroides and Thalassodendron ciliatum) invest two to 
four times more energy into below-ground biomass 
growth than the colonizing species (Halodule uninervis, 
Cymodocea rotundata and Cymodocea serrulata)"’. 
Biomass values show high variability (Table 16.1] due to 
habitat differences, species composition, plant densities 
between locations and sampling techniques’. 

Manila Bay 



epulsuan BRUNE! <’ 


MALAYSIAJ — Anambas 
: \ 


=< Sha. - Riu 
i) acl 

cae Archipelago 
., Bangka 


‘Sumatra « 

“Belitung 4 f 

Lampung Bay 
Kepulauan Seribu 4 
Gremang Bay JAVA SEA 

gow Jakarta Bay 
Sunda Strait—— 52, Jakarta 
Banien Bay “s 

& P 
° Kangean 



Gilmanuk Bay 
0 200° 400 +600 800 1000 Kilometers 
—— a 
Gerupuk Bay! 
Map 16.1 

Seagrass density also varies considerably 
between locations (Table 16.2]. Kiswara found that the 
density of Halodule uninervis depends on the phenotype 
(normal shoots or thin shoots). In Gerupuk Bay, 
southern Lombok, Halodule uninervis densities ranged 
from 870 normal shoots/m’* to 6 560 thin shoots/m? 
within the same seagrass bed". Nienhuis reported that 
Halodule uninervis had the highest density of all 
seagrass species in mixed as well as in monospecific 
seagrass beds (Table 16.3). In seagrass beds where 
foliage covers more than 70 percent of substrate, the 
density of seagrasses frequently depends on the 
species composition of the community and the relative 
age of the seagrasses. In some species, such as 
Thalassia hemprichii, biomass is frequently a function 
of shoot density and total leaf area per leaf cluster”. 

Seasonal studies of seagrass biomass and shoot 
densities in Indonesian waters are scarce but 
significant seasonal fluctuations are known to occur”. 


Growth studies have been carried out in Indonesia 
using several techniques” * '*'”. Using the oxygen 
evolution [photosynthesis] technique, Lindeboom and 
Sandee’ demonstrated that gross primary production 
rates of various seagrass communities in the Flores 
Sea vary from 1230 mg carbon/m’/day to 4700 mg 
carbon/m*/day. Seagrass respiration consumption 
rates were between 860 mg carbon/m‘*/day and 3900 
mg carbon/m*/day. They concluded that net primary 
production rates of seagrass communities in the Flores 

Puerto Galera 

Spermonde P e 
Arcipelago YL BANDA SEA *, 

Flores Sea pi 





= + =« 
= Aes 
af ~* Fyor0ng . 
oo - 

Sulawesi, Ceram Sea sg: 

Kotania Bay 

Ambon Bay oe 


= Taka Bone Rate Atoll Pe 

~ rer 



Lesser Sunda Islands 

Table 16.3 
Average shoot density of seagrass species in mixed and 
monospecific seagrass meadows in the Flores Sea 
Species Mixed seagrass Monospecific seagrass 
meadow (number meadow [number 
of shoots/m’] of shoots/m’} 

324 (276) = 

696 (767) 533 (543) 

54 (86) 136 (58) 
Halodule uninervis 2847 (5689) 14762 (6 076) 
Halophila ovalis 69 (117) - 
Syringodium isoetifolium 2504 (1736) - 
Thalassia hemprichii 754 [748] 1459 (811) 
Thalassodendron ciliatum - 692 (272) 

Cymodocea rotundata 
Cymodocea serrulata 
Enhalus acoroides 

Note: In all sampling locations foliage cover is >70 percent, 
except for Thalassodendron ciliatum (>50 percent } [SD in 

Sea vary between 60 mg carbon/m’/day and 1060 mg 
carbon/m?/day which, assuming the same rates of 
production throughout the year as during the study 
period (October), translates to a maximum annual net 
primary production of about 387 g carbon/m’. Epiphyte 
production alone accounted for a maximum annual net 
primary production of about 84 mg carbon/m‘ of leaf 
surface area”, or 36 percent of the net primary 
production rate of the seagrass communities studied. 



ee een 

A comparative study of two different seagrass 
environments in the Spermonde Archipelago obtained 
very similar results using the same techniques". 
Gross primary production rates ranged from 900 mg 
carbon/m*/day to 4400 mg_ carbon/m‘/day. 
Interestingly, the bell-jar technique used in the 
Spermonde Archipelago did not reveal any significant 
difference in seagrass production rates between 
coastal and reef environments. Net primary 
production was slightly negative in a number of 
stations and was. generally below 500 mg 
carbon/m‘/day. Low net primary rates were attributed 
to high community oxygen consumption rates. Higher 
net primary production rates were obtained from 
monospecific stands of Thalassia hemprichii, where 
combined seagrass and epiphyte net production rates 
reached 1.5 mg carbon/m’/day to 1.9 mg 
carbon/m‘/day, equivalent to a maximum of 694 mg 

Nienhuis has suggested that Indonesian seagrass 
communities are self-sustaining systems and export 
very little of their photosynthetically fixed carbon to 
adjacent ecosystems such as coral reefs”. The results 
obtained from the Flores Sea and Spermonde 
Archipelago seem to support this general hypothesis. 
Erftemeijer points out that many seagrass communities 
(58 percent of his study sites] seem to use more energy 
than is actually produced by the autotrophic seagrass 
community. This suggests that, while recycling of nutri- 
ents and organic carbon is high, seagrass beds may not 
be self-sustaining. Filter and suspension-feeding 
macroinvertebrates constitute a significant consumer 
component of the Indonesian seagrass community. 

Marking methods have been used to measure leaf 
production’ in seagrass meadows at Taka Bone Rate 
Atoll”, Kepulauan Seribu'™”: \“’, Banten Bay'”' and, most 
recently, in Lombok'® and the Spermonde 

Table 16.4 
Average growth rates (mm/day) of seagrass leaves using leaf-marking techniques 

Species West Java 


Archipelago”. Production rates obtained from these 
studies are summarized in Table 16.4. 

Erftemeijer” demonstrated that, while there was 
no difference in primary production rates of coastal and 
offshore seagrass beds in Sulawesi, the leaf growth 
rate (3.1 mm/day) of Enhalus acoroides was 
significantly higher in muddy coastal habitats than in 
offshore reef habitats (1.6 mm/day]. Similar results 
were obtained for Thalassia hemprichii. 


Seagrass-associated flora and fauna remain one of the 
most open and exciting fields of research for Indonesian 
scientists. Recent studies have focused on establishing 
species lists and measuring abundance and biomass of 
various seagrass-associated taxa. With a few 
exceptions’ “” the majority of seagrass-associated 
faunal studies have dealt with infauna, macrofauna, 
motile epifauna and epibenthic fauna [Table 16.5). 


Fishermen at Benoa, Bali and West Lombok have 
recorded seven economically important species of 
seaweeds growing in the mixed seagrass meadow of 
Cymodocea serrulata, Halodule uninervis, Thalassia 
hemprichii and Thalassodendron ciliatum””. In South 
Sulawesi 117 species of macroalgae are associated 
with seagrasses, composed of 50 species of 
Chlorophyta, 17 species of Phaeophyta and 50 species 
of Rhodophyta. Thirteen species were exclusively 

associated with seagrass vegetation”. 


The meiofauna associated with monospecific Enhalus 
acoroides seagrass beds on the south coast of Lombok 
consisted of nematodes, foraminiferans, cumaceans, 

copepods, ostracods, turbelarians and polychaetes”, 

Lombok Flores 

Sea Archipelago 

Cymodocea rotundata - 
5.0 (0.6) 
7.3 (3.6) 

Cymodocea serrulata 
Enhalus acoroides 

Syringodium isoetifolium 4.1 (6.8) 
Thalassia hemprichii 4.9 (1.5) 
Thalassodendron ciliatum = 

Production rates in parentheses (g dry weight/m*/day). 
* In mg ash-free dry weight/m?/day. 

2.4 (2.3*) 

1.6 (3.5") 

= 5.5 (6.8) 

6.5 (1.5) 
3.8 [8.1] 5 
2.7 (4.7) 

Table 16.5 
Indonesian seagrass-associated flora and fauna: number of species 

Taxon Banten Bay Jakarta Bay Lombok 
Algae 37 

Mollusks 55 
Crustaceans 84 
Echinoderms 45 
Fishes 85 
Fish larvae 53 

Source: Various sources” 

many of which were actively emergent. A high 
abundance of nematodes was indicative of nutrient 
enrichment. Benthic foraminifera are an important 
component of Indonesian seagrass communities, but 
have received only rudimentary attention”. In the 
Kepulauan Seribu patch reef complex, seagrass beds 
are abundant and frequently dominated by associations 
of Enhalus acoroides and Thalassia hemprichii*”'. 
Benthic foraminifera in this location are dominated by 
the suborders Miliolina and Rotaliina’. The most 
abundant rotaliinids were Ammonia beccarii, Ammonia 
umbonata, Calcarina calcar, Elpidium advenum, 
Elpidium crispum, Elpidium craticulatum and Rosalina 
bradyi. The genus Ammonia is a euryhaline group, 
common in shallow-water tropical environments, and 
Calcarina calcar is indicative of coral reef habitats. The 
abundance of Elpidium spp. is interesting, since this 
euryhaline, shallow-water species is extremely tolerant 
of low salinities and can be found far up estuaries. The 
miliolinids are represented by Adolesina semistriata, 
Milionella sublineata, Quinqueloculina granulocostata, 
Quinqueloculina parkery, Quinqueloculina_ sp., 
Spiroloculina communis, Spirolina cilindrica and 
Triloculina tricarinata. Both Quinquiloculina and 
Triloculina are characteristic of shallow tropical waters. 


Crustaceans are a key component of seagrass food 
webs. Recent gut analyses from the south coast of 
Lombok" demonstrated that crustaceans are the 
dominant food source for seagrass-associated fish. 
Aswandy and Hutomo'" recorded 28 species of 
crustaceans in Banten Bay seagrass beds. The 
tanaidacean Apseudes chilkensis and an unknown 
species of melitidae amphipod are the most abundant 
crustaceans in Enhalus acoroides meadows in 
Grenyang Bay”. Moosa and Aswandy”™” recorded 70 
crustacean species from seagrass meadows in Kuta 
and Gerupuk Bays but many specimens were 

6 groups 


Ambon Bay Kotania Bay South Sulawesi 

34 117 

143 [hermit crabs} 


apparently collected from coral rubble areas adjacent 
to the seagrass meadows. One hipollitid shrimp there, 
Tozeuma spp., has special morphological adaptations 
to live specifically in seagrass meadows. Its lancelet 
body shape and coloration, green mottled with small 
white spots, provides almost perfect camouflage when 
it adheres to seagrass leaves. Many stomatopods are 
found in Indonesian seagrass beds with Pseudosquilla 
ciliata, an obligate seagrass-associated species'”. 
Other stomatopods, such as Odontodactylus scyllarus, 
leave the reefs to forage for mollusks in adjacent 
seagrass beds”. Rahayu collected 30 species of hermit 
crabs from Kotania Bay seagrass bed. Three were 
species of Diogenes, one was a species of Pagurus and 
four were undescribed species. It is believed that 
crustaceans in the seagrass beds of Kotania Bay are 
much more diverse than those of other locations. 

The mollusks are one of the best-known groups of 
seagrass-associated macroinvertebrates and perhaps 
the most overexploited. Mudjiono et al. recorded 11 
gastropods and four bivalves from the seagrass 
meadows in Banten Bay”!. This rather impoverished 
mollusk fauna was collected from monospecific Enhalus 
acoroides beds, in mixed beds of Enhalus acoroides, 
Cymodocea serrulata and Syringodium isoetifolium, and 
mixed beds of Enhalus acoroides, Cymodocea rotundata, 
Cymodocea serrulata, Halodule uninervis, Halophila 
ovalis, Syringodium isoetifolium and _ Thalassia 
hemprichii. The entire bay is heavily exploited and only 
two gastropods were common to all locations, Pyrene 
versicolor and Cerithium tenellum. Just four juvenile (3- 
5 mm diameter] Trochus niloticus were collected”. 
Seventy species were collected from less 
disturbed sites in Lombok’, many of which are 
economically valuable. Gastropod families included 
Bullidae, Conidae, Castellariidae, Cypraeidae, Olividae, 
Pyrenidae, Strombidae, Trochidae and Volutidae; 




bivalve families were Arcidae, Cardiidae, Glycymeri- 
dae, Isognomonidae, Lucinidae, Mesodesnatidae, 
Mytilidae, Pinnidae, Pteridae, Tellinidae and Veneridae. 
Pyrene versicolor, Strombus labiatus, Strombus 
luhuanus and Cymbiola verspertilio were the most 
abundant gastropod species and Anadara scapha, 
Trachycardium flavum, Trachycardium subrugosum, 
Peryglypta crispata, Mactra spp. and Pinna bicolor were 
the most common bivalve species””. A number of Conus 
species were found. 

A high diversity of mollusks, 142 species from 43 
families, has also been reported from seagrass beds in 
Kotania Bay’. 

The most significant echinoderm species is a sea star, 
Protoreaster nodosus, which feeds on seagrass 
detritus and the surface of broken seagrass leaves. 
Forty-five species of Echinodea, Holothuridae, Ophiur- 
oidae and Crinoidae have been recorded in the 
seagrass beds of Kuta and Gerupuk Bays. Several 
economically important species of Holothuria and 
Actinopyga, and the sea urchin Tripneustes gratilla, 
have declined in abundance”. 

Similar depletions in echinoderm populations 
have been reported from Kotania Bay on west Ceram 

Case Study 16.1 

Banten Bay covers 120 km?, and harbors several 
coral islands. The biggest inhabited island is Pulau 
Panjang; the other islands are small and uninhabi- 
ted. The rivers Domas, Soge, Kemayung, Banten, 
Pelabuhan, Wadas, Baros and Ciujung discharge 
into the bay. Seagrass is found along the mainland 
Java coast in the western part of the bay, on the reef 
flat of the coral islands (Pulau Panjang, Pulau 
Tarahan, Pulau Lima, Pulau Kambing and Pulau 
Pamujan Besar] and on submerged coral reefs in 
the intertidal area down to a depth of 6 m. The total 
area of seagrass beds at Banten Bay is about 330 ha, 
consisting of 168 ha on the mainland and 162 ha on 
the coral islands. 

The depth of the bay is not more than 10 m. Its 
sediment consists of mud and sand” *) and the 
salinity varies between 28.23 and 35.34 psu. The 
rainy season Is from November to March. Mangrove 
is found at Grenyang in the eastern part of the bay up 
to Tanjung Pontang in the west part, and in the 
southern part of Pulau Panjang. Eight species of 
seagrasses occur here: Cymodocea rotundata, 
Cymodocea serrulata, Enhalus acoroides, Halodule 

Island, Moluccas, where seagrass meadows formerly 
supported a high abundance of economically important 
holothuroids. In 1983, the extensive seagrass meadows 
in Kotania Bay supported high population densities [i.e. 
1-2 individuals/m’) of nine economically important sea 
cucumber species, namely Bohadschia marmorata, 
Bohadschia argus, Holothuria (Metrialyta) scabra, 
Holothuria nobilis, Holothuria vagabunda, Holothuria 
impatiens, Holothuria edulis, Thelenota ananas and 
Actinopyga miliaris. In a 1993 inventory of the same 
area, only three sea cucumbers were recorded within a 
distance of 500 m. The average body size of sea cucum- 
bers decreased from around 22 cm in 1983 to less than 
15 cm in 1993. The decline of the stock and size are 
attributed to intensive collections by local people to 
supply the lucrative teripang (béche de mer) trade. 
Another heavily overexploited echinoderm species 
whose population has declined sharply during the past 
ten years is the edible sea urchin Tripneustes gratilla. 


In 1977 one of the first studies of seagrass-associated 
fish in Indonesia collected 78 species from Thalassia 
hemprichii and Enhalus acoroides meadows amongst 
lagoonal patch reefs in Pari Island, in the Kepulauan 
Seribu complex”. Only six (Apogonidae, Atherinidae, 

uninervis, Halophila ovalis, Halophila minor, 
Syringodium isoetifolium and Thalassia hemprichii. 
Beds between 25 and 300 m in length" are 
continuous along the coast of Banten Bay, from the 
beach to the reef edge. 

They are nursery grounds for 165 species of 
fish which feed either directly on algae and 
seagrass or on seagrass-associated inverte- 
brates), including six juveniles of grouper 
(Epinephelus bleekeri, Epinephelus fuscoguttatus, 
Epinephelus merra, Epinephelus septemfasciatus, 
Epinephelus coioides and Plectropomus spp.'*)). 
Dugongs also occur here“. The cultivation of 
seaweeds in Banten Bay has increased enormously 
in recent years along the coastline of all the islands, 
on the coral reef and lately also outside the reef flat 
area. Approximately 35 ha, including 25 ha or 10 
percent of the reef flat area and 10 ha outside the 
coral reef flat, are now used for the cultivation of 
seaweeds and have been cleared of seagrass'”. 
Transplantation studies using Enhalus acoroides 
were conducted in Banten Bay in 1998". Only 
rhizomes transplanted to muddy substrate survived 
more than five months — these new seagrass beds 
are now used by local fishermen to collect fishes 
and prawns). 

Labridae, Gerridae, Siganidae and Monacanthidae) of 
the families recorded, however, could be considered as 
important seagrass residents. The Pari Island study 
was followed in 1985 by a long-term study of seagrass 
fish assemblages in Banten Bay, southwest Java Sea. 
The results from the Banten Bay study’ supported 
earlier views that only small numbers of fish species 
permanently reside in seagrass beds. However, it was 
also reconfirmed that seagrass beds act as nursery 

Case Study 16.2 

Kuta and Gerupuk Bays are covered by gravel, small 
pebbles, fine sand and mud in the river mouth, 
where Enhalus acoroides grows. The tidal range in 
the bays is about 2 m, tidal velocity and direction are 
2.8-10.8 cm/min and 315°-350° at high tide and 4.5- 
10.0 cm/min and 270°-310° at low tide. During the 
wet season, December to April, salinity varies from 
28 to 29 psu and surface water temperature from 18 
to 24°C. In the dry season, May to November, these 
measurements are approximately 34 psu and 27°C. 

The most diverse seagrass beds in Indonesia 
occur here, with 11 of the 12 species present in 
Gerupuk (Cymodocea rotundata, Cymodocea serru- 
lata, Enhalus acoroides, Halodule pinifolia, Halodule 
uninervis, Halophila minor, Halophila ovalis, 
Halophila spinulosa, Syringodium isoetifolium, 
Thalassia hemprichii, Thalassodendron ciliatum). 
Halophila spinulosa is absent from Kuta. Enhalus 
acoroides and Thalassodendron ciliatum form 
monospecific beds in both bays, and Halophila 
spinulosa in Gerupuk Bay. Mixed beds of Cymodocea 
rotundata, Cymodocea serrulata, Halodule pinifolia, 
Halodule uninervis, Halophila minor, Halophila 
ovalis, Syringodium isoetifolium and Thalassia 
hemprichii occur at both locations. 

Coverage area of habitat types at Kuta and Gerupuk Bays 

Coverage area (ha) 
Kuta Bay Gerupuk Bay 

Enhalus acoroides 7.68 29.40 
Thalassodendron ciliatum 10.50 id 
Halophila spinulosa 11.07 
Habitat types 

Mixed vegetation 76.86 
Sandy bar 42.97 
Lagoon = 
Dead coral 27.36 
Live coral = 
Volcanic stone - 


grounds for many economically valuable fish species. 
Beds with higher densities of seagrass supported 
higher abundance of fish, and Enhalus acoroides 
meadows supported higher fish abundance than 
Thalassia hemprichii. 

Studies on seagrass fish in Indonesia have been 
gradually increasing since the late 1980s‘ %*°7). 
Indonesian seagrass fish communities are commonly 
dominated by Siganidae [rabbitfishes], such as Siganus 

Large amounts of seagrass detritus wash up 
and accumulate on the beach during the strong 
winds of the east monsoon. Interestingly Thalasso- 
dendron ciliatum at Kuta Bay is able to grow on 
volcanic stone. During low tide the local community 
collects milkfish, sea cucumbers, octopus, shellfish, 
sea urchins and seaweeds (Caulerpa spp., Gracilaria 
spp. and Hypnea cervicornis) from the seagrass 
beds. The commercial alga, Kappaphycum alvarezi, 
is cultivated here. 

Associated flora and fauna of the seagrass bed of Lombok 

Taxon group Number of species 
Algae 37 
Meiofauna™” 6 (higher taxa) 
Mollusk”" 55 
Echinoderm”” 45 
Crustacean” vi) 

Fish”! 85 

Fish larvae 53 

Source: Various sources - see references by groups. 

Only four of the fish found here - 
Syngnathoides biaculeatus, Novaculichthys spp., 
Pervagor spp. and Centrogenys valgiensis — are typi- 
cal seagrass fishes. Halichoeres argus and Cheilio 
enermis are abundant not only in seagrass but also 
in algal beds. The dominance of Syngnathoides 
biaculeatus and Cheilio enermis is unusual because, 
more commonly, the fish populations of Indonesian 
seagrass beds are characterized by abundant 
rabbitfish, especially Siganus canaliculatus. 

The main threat to the seagrass of Kuta and 
Gerupuk Bays is the intensive collecting of intertidal 
organisms during low tide, often involving digging 
with sharp iron sticks which disturb the substrate, 
cut the leaves of seagrasses and uproot their 
rhizomes. Future threats may include hotel 
construction and operation as the area has been 
earmarked for development by the local 




Case Study 16.3 

Kotania Bay, Ceram Island, contains five small 
islands: Buntal, Burung, Marsegu, Tatumbu and Osi. 
Only Osi has freshwater and Is inhabited, along with 
two villages at Pelita Jaya and Kotania on Ceram 
Island. The water around Pelita Jaya (40 m) is 
deeper than that at Kotania village (20 m). The 
intertidal area in the northern part of Kotania Bay is 
very narrow [4 to 10 m) but wider in the east and 
south (50 to 250 m). Seagrasses are found along the 
whole coast area of the bay, except in the north. On 
Buntal and Osi Islands the sediment trapped by 
these seagrass beds has, over time, created “cliffs” 
which have served as substrate for the development 
and seaward expansion of mangrove communities. 
The seagrass beds have been mapped using 
remote-sensing techniques which estimated a total 
area of 11.2 km’. The pattern of seagrass 
distribution depends on the type of substrate. 
Muddy substrate is mostly dominated by 

Table 16.6 
Present coverage of seagrasses in Indonesia 
E) Geass 
eee ca 
a << ed 
Coverage (hal 200-300 50-150 <2 5-150 
Cover (%] 20-80 15-80 12-25 10-15 5 
Recorded species [number] 9 8 5 7 
Enhalus acoroides C A R R 
Halophila decipiens - - - - 
Halophila minor - - - VR 
Halophila ovalis R R R VR 
Halophila spinulosa = = = = 
Thalassia hemprichii C VA C R 
Cymodocea rotundata R C R VR 
Cymodocea serrulata R R - = 
Halodule pinifolia R R = VR 
Halodule uninervis R R = = 
Syringodium isoetifolium R C VR VR 
Thalassodendron ciliatum C = = = 

Notes: C common; A abundant; R rare; VA very abundant; VR very rare. 

Lampung Bay 

aoa i 

aw wD 

monospecific beds of Enhalus acoroides. Mixtures 
of mud, sand and coral rubble are usually covered by 
Thalassia hemprichii. The highest density of 
seagrass IS found in the area between Osi and 
Burung. The eastern part of the bay, called Wai Tosu, 
has two kinds of substrates. The sediment at the 
mouth of a small creek is deep and muddy, and is 
covered only by Enhalus acoroides {10-20 percent 
coverage} while there is a thin layer of mud, sand 
and coral rubble about 100 m in front of the 
mangroves. Underneath this thin substrate is a hard 
layer of coral rock. Thalassia hemprichii, Cymod- 
ocea rotundata, Halodule uninervis, Halophila ovalis 
and Enhalus acoroides grow sporadically here to 
less than 35 percent coverage. Local people have Set 
a fish trap around the seagrass area and bullt a 
large cage to rear sea cucumbers. 

In the southern part of Kotania Bay the 
intertidal zone is very flat and almost all is exposed 
during the lowest tides. The substrate near to the 
mangrove area is mixed mud and sand dominated by 
Thalassia hemprichii and Enhalus acoroides. Along 

2 a 
Bat coke ee aT = 
BO ne es Ek, aay tasters 
S 2 = PS 8 = > 
o o = = oS s 5 
ao ao e Oo a ee oO 
05-18 336 20-80 30 1 73 36 
5-15 25-45 30-70 15-50 5-10 30-70 20-50 
9 Beato 5 9 10 1 
© WA 2 R R VA VA 
= = R ~ = = = 
= R R = S R R 
R R R R R R R 
= - = 2 E = R 
R R R R R R R 
vR VR R = R R R 
R = R = R R R 
R R R R R R R 
R R R = R R R 
c = A = R c R 

Indonesia 179 

Distribution of seagrass in Kotania Bay 

Species of seagrass % cover Substrate type Depth (m) PJ TL Ol BRI BTI Tl Ml 
Cymodocea rotundata 10-40 Sand +0.2-2.0 v v v Vv v v v 
Cymodocea serrulata <5 Sand 0.5-2.0 v v v, 
Enhalus acoroides 20-60 Mud, sand 0.5-2.5 v v J v v v v 
Halodule pinifolia <5 Sand +0.2-1.5 v v v v / v 
Halodule uninervis <5 Sand 0.5-2.0 v v v v v v v 
Halophila decipiens 40-100 Coral rubble v J 
Halophila ovalis <5 Sand +0.2-1.5 v v v v v v v 
Halophila minor J 

Syringodium isoetifolium <5 Mud, sand 0.5-2.0 v v v / 
Thalassia hemprichii <5 Mud, sand +0.2-2.5 v / v J v 

Notes: PJ Pelita Jaya; TL Tanjung Lalansoi; 0! Osi Island; BRI Burung Island; BT! Buntal Island; Tl Tatumbu Island; Ml Marsegu Island 

the southern part of the bay up to Tanjung Lalansoi lata, Halodule pinifolia, Halodule uninervis, Halophila 
the substrate in the deeper areas is a mixture of sand ovalis and Enhalus acoroides. The seagrass density 
and coral rubble. The most common seagrasses is quite high and varies seasonally. Percent coverage 
there are Thalassia hemprichii, Cymodocea rotun- ranges from 40 to 70 percent with the highest values 
data, Syringodium isoetifolium, Cymodocea serru- always close to the mangrove areas. 

a 2 
wo = is a = cy) 4 = <7 a £ 
Seller, aE. ee ae Eh a Ce yt en 
aoa Se Meas kt ee, ere oe ee Rea ne aie 2 
Seen ee ee Beene a) a ad epee | ia 
a <= a =< o = = = a = = = 
Coverage (hal 10-50  0.3-1 4-5 212 25-75 100-1000 5-50 10-100 25-75 100-1000 5-50 10-100 
Cover (%] 30-60 5-20 15-30 30-80 30-60 50-99 30-70 30-50 30-60 50-99 30-70 30-50 
Recorded species (number) 9 7 8 10 8 8 8 8 8 8 8 8 
Enhalus acoroides VA R R A VA A VA VA VA A VA VA 
Halophila decipiens - - - R - - - - - - - - 
Halophila minor R VR = R - = = = = = = = 
Halophila ovalis R R R R R R R R R R R R 
Halophila spinulosa - - - - = = = = - = = - 
Thalassia hemprichii VA C R VA VA R VA VA VA R VA VA 
Cymodocea rotundata R C C C R R R R R R R R 
Cymodocea serrulata R - R R R R R R R R R R 
Halodule pinifolia R VR R R VR R R R VR R R R 
Halodule uninervis R R R R R R R R R R R R 
Syringodium isoetifolium R - R C R R R R R R R R 


Thalassodendron ciliatum 

Notes: C common; A abundant; R rare; VA very abundant; VR very rare. 


Photo: P. Erftemeijer 

canaliculatus in Jakarta Bay'”, except in Lombok (see 

Case Study 16.2). Indonesian seagrass fish have been 

classified into four principal species assemblages: 

1 permanent residents which spend most of their 
lives in seagrass beds (e.g. the chequered 
cardinalfish, Apogon margaritophorus); 

2 residents which live in seagrass throughout their 
life cycle but which spawn outside the seagrass 
beds [e.g. Halichoeres argus, Atherinomorus 
duodecimalis, Cheilodipterus quinquelineatus, 
Gerres macrosoma, Stephanolepis hispidus, 
Acreichthys hajam, Hemiglyphidodon plagio- 
metopon, Syngnathoides biaculeatus); 

3 temporary residents which occur in seagrass 
beds only during their juvenile stage (e.g. Siganus 
canaliculatus, Siganus virgatus, Siganus punc- 
tatus, Lethrinus spp., Scarus spp., Abudefduf 
spp., Monacanthus chinensis, Mulloidichthys 
flavolineatus, Pelates quadrilineatus, Upeneus 

4 occasional residents or transients that visit 
seagrass beds to seek shelter or food. 

Measuring the primary productivity of seagrass meadows in 
Sulawesi using enclosures equipped with oxygen electrodes 

The first study on seagrass fish larvae and 
juveniles took place in Kuta Bay and recorded 53 
species belonging mainly to four families: Channidae, 
Ambassidae, Engraulidae and Gobiidae. High numbers 
of species and individuals were found in unvegetated 
areas full of broken seagrass leaves, and in the Enhalus 
acoroides beds. 


Herbarium collections of seagrasses from Indonesian 
waters were made by Zollenger in 1847 and 
Kostermans in 1962 and include both Ruppia maritima 
from Ancol-Jakarta Bay and Pasir Putih, East Java, and 
one specimen of Halophila beccarii from an unknown 

location. The development of Jakarta has destroyed the 
Mangrove swamp in Ancol, the only place that Ruppia 
maritima had been reported, and this is thought to have 
caused the disappearance of this species from 

For 15 years the Ancol Oceanorium in Jakarta kept 
two male dugongs in captivity, feeding them with 
seagrasses [(Syringodium isoetifolium and Halodule 
uninervis) harvested from Banten Bay. Unfortunately 
they died in November 1991”. There is one female 
dugong in Surabaya Zoo, which has been in captivity 
since 1985. Its food is harvested from Celengan- 
Muncar, East Java, about 340 km from Surabaya. It 
feeds mostly on Syringodium isoetifolium, which forms 
95 percent of the dugong’s dietary intake. The con- 
sumption rate of the captive dugong is approximately 30 
kg wet weight/day“". Recently Sea World of Indonesia in 
Ancol-Jakarta has acquired two male dugongs. One of 
them was caught in seine nets in Banten Bay in 1998 
and the other one was trapped in a sero [fish trap) on 
the seagrass bed at Miskam Bay in 2001. 

The degradation of seagrass beds in Indonesian 
waters has been poorly documented from only limited 
areas. The decline of seagrass beds at Banten Bay was 
caused by converting agricultural areas and fish ponds 
into an industrial estate, with a total loss of about 116 
ha or 26 percent of seagrass mainly in the western part 
of the bay'’. The decline of other seagrass beds has 
been caused by reclamation activities. Less damaging 
than the reclamation was the uprooting of seagrasses 
by fishing boats using seine nets to catch shrimp and 
fish”. In Kuta and Gerupuk the decline of seagrass was 
caused by people collecting dead coral for building 
material in the seagrass beds. 


It is difficult to present accurate information about the 
present coverage of Indonesian seagrass, since 
observations on seagrass ecosystems in Indonesia vary 
considerably in duration, location, method of sampling 
and object of study, and many places in Indonesia have 
not been studied yet. Table 16.6 summarizes existing 
knowledge about the present coverage in Indonesia. 
Based on this available information, and to the best of 
our knowledge, we estimate that seagrass covers at 
least 30000 km’ throughout the Indonesian 

Seagrasses in Indonesia are presently threatened 
mainly by physical degradation such as mangrove 
cutting and coral reef damage, and by marine pollution 
from both land- and marine-based sources, and by 
overexploitation of living marine resources such as fish, 
mollusks and sea cucumbers. The alarming amount of 
land reclamation is an increasing cause of seagrass 
habitat loss in Indonesia. 


No specific regulation relating to seagrass is currently 
available and so management is implemented through 
general regulations pertaining to marine affairs, 
environmental protection and management of living 
resources. Of primary importance is the Act of the 
Republic of Indonesia {RI} No. 5 1990, concerning the 
conservation of living resources and their ecosystems, 
together with Act of the RI No. 5 1994 on the ratification 
of the Convention on Biodiversity and Act of the RI No. 
23 1997 concerning the management of the living 
environment. Apart from acts and statutes, there are 
three other types of regulation which are hierarchically 
lower than the former: they are government regulation, 
presidential decree and ministerial decree. 

To have a proper management system for 
coastal ecosystems, appropriate laws and regulations 
must be established. The Indonesian Seagrass Com- 
mittee [ISC) has therefore prepared a draft Seagrass 
Policy, Strategy and Action Plan to guide the manage- 
ment of the seagrass ecosystem in Indonesia. It forms 
an integral part of the activities of the South China Sea 
Project, financed by UNEP-GEF [the United Nations 
Environment Programme section of the Global 
Environment Facility], and seeks to address the main 
issues concerning the management of seagrasses. 
The draft, scheduled to be completed in 2004, is 
expected to become a reference document in the 
formulation of official regulations by the government. 


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Regional map: Asia 






< SEA 




: 0 300 600 900 1200 1500 km 

100° 115° 



Photo: J.S. Bujang 

Halophila decipiens female [right] and male (left) 

flowers, Malaysia 

Photo: J.S. Bujang 

Enhalus acoroides in Malaysia and 
Indonesia: female flowers [above]; pollen on 
the water surface (right, top); fruit (right, Spadix of eelgrass, Zostera marina, with male 

middle]; seed dispersal (right, bottom} flowers releasing pollen 

Photo: J.S. Bu 

Thalassia hemprichii fruit 

The seagrasses of 

The Philippines and Viet Nam 

The Philippines and Viet Nam 

Philippine Archipelago. There are documented 

sizeable beds offshore from western, north- 
western and southern islands covering 978 km’ at 96 
well-studied sites. Approximately one third of this area 
has been mapped in detail using a combination of 
remote sensing and field survey techniques. The 
remainder is estimated. With many other areas not 
surveyed for seagrasses, the total seagrass area is 
likely to be many times greater. 

The Philippines is reported to have 15 species of 
seagrass. In addition to Ruppia maritima and 
Halophila beccarii, Fortes lists a new variety of Halophila 
minor”. Calumpong and Menez" consider Halophila 
beccarii to have been extirpated from Philippine waters, 
because the only specimens to be collected were in 1912 
from Manila Bay”, now heavily impacted by the growth 
of metropolitan Manila. Fortes disagrees, believing this 
species still occurs in Manila Bay” and to be common in 
Lingayen Gulf, northwestern Philippines. 

Many plants and animals live in the seagrass 
beds of the Philippines and Viet Nam, supporting 
fisheries with their rich nutrient pool and the diversity 
of physical structures protecting juveniles from 
predators. Major commercial fisheries occur 
immediately adjacent to seagrass beds". Fish and 
shrimp are the most important elements of the 
commercial fishery, although coastal villages derive 
their sustenance from other components of the grass 
beds. The major invertebrates found in the beds are 
shrimps, sea cucumbers, sea urchins, crabs, scallops, 
mussels and snails. Some endangered species of sea 
turtles reported in seagrass beds include the green sea 
turtle, the olive Ridley, the loggerhead and the flatback. 
In the Philippines and Viet Nam the sea cow (Dugong 
dugon), which is almost completely dependent on 
seagrass, IS an endangered species. 

Coral reefs and their associated seagrasses 
potentially supply more than 20 percent of the fish 

Gries are found extensively throughout the 

catch in the Philippines. A total of 1384 individuals and 
55 species from 25 fish families were identified from 
five seagrass sites!” 

Calumpong and Menez” describe two mixed 
species associations, one of Syringodium (or 
sometimes Thalassia) with Cymodocea and Halodule 
spp., growing primarily on sandy sediment, the other of 
Enhalus and Thalassia spp. on muddy substrates. 
Monospecific seagrass beds are less common than 
mixed populations in the Philippines and tend to occur 
under certain conditions: Enhalus acoroides colonizes 
turbid, quiet, protected areas such as bays and 
estuaries and Thalassia hemprichii occurs as pure 
stands in the tidepools of the most northerly islands in 
the Philippines'"'. Halophila decipiens grows primarily 
at depths of 11-23 m'”. Thalassodendron ciliatum and 
Halophila spinulosa are found in deep, clear water”. 
Thalassodendron ciliatum also grows in shallow waters 
but only in conditions of low turbidity on coarse or rocky 
substrates”. Cuyo Island is the northernmost limit of 
Thalassodendron ciliatum in the Pacific’. 

The vital role of seagrasses as nursery grounds 
and food for fish and invertebrates in the Philippines 
has been appreciated for some time!”. The rabbitfish, 
Siganus canaliculatus, is a voracious herbivore and 
particularly important as a food species. In Bais Bay, 
Negros Oriental, the population of Siganus 
canaliculatus consumes 0.64 metric tons per day from 
a 52-ha Enhalus acoroides meadow'”. However, this 
represents less than 1 percent of the daily organic 
production of Enhalus acoroides. Rabbitfish are often 
caught in seagrass beds using bamboo traps”, 
representing a direct link between seagrass habitat and 
human subsistence. 

Seagrass beds in the Philippines are threatened 
by eutrophication, siltation, pollution, dredging and 
unsustainable fishing methods. Many thousands of 
hectares of seagrass have been lost as a result of land 
reclamation for housing, airports and shipping 


Photo: M. Kochzius 


Spear-fisher over a seagrass bed in the Philippines 

facilities”. Some attempts have been made at 

rehabilitating damaged seagrass beds _ using 

transplanting techniques'™”’. 

Puerto Galera, a quiet ecotourist destination 
south of Manila, is the site of one of the first 
SeagrassNet global monitoring locations. Quarterly 
sampling of the seagrass habitat has been conducted 
at reference and impacted seagrass sites monitored by 
graduate students from the University of the 
Philippines. Even in the early stages of monitoring the 


1 Mefiez EG, Phillips RC, Calumpong HP [1983]. Seagrasses from the 
Philippines. Smithsonian Contributions to the Marine Sciences No. 
21. pp 1-40. 

2 Mefiez EG, Calumpong HP [1983]. Thalassodendron ciliatum: An 
unreported seagrass from the Philippines. Micronesia 18: 103-111. 

3 Menez EG, Calumpong HP [1985]. Halophila decipiens: An 
unreported seagrass from the Philippines. Proceedings of the 
Biological Society of Washington 98(1): 232-236. 

4 Fortes MD [1990]. Seagrass resources in East Asia: Research 
status, environmental issues and management perspectives. In: 
ASEAMS/UNEP Proceedings of First ASEAMS Symposium on 
Southeast Asian Marine and Environmental Protection. UNEP 
Regional Seas Reports and Studies No. 116. pp 135-144. 

5 Fortes MD [1986]. Taxonomy and Ecology of Philippine Seagrasses. 
PhD dissertation, University of the Philippines, Diliman, Quezon 
City. 245 pp. 

6 Short FT, Coles RG (eds) [2001] Global Seagrass Research 
Methods. Elsevier Science, Amsterdam. 

7 Fortes MD [1989]. Seagrasses: A Resource unknown in the ASEAN 
Region. ICLARM Education Series 5. 46 pp. 

8 Calumpong HP, Mefiez EG [1997]. Field Guide to the Common 
Mangroves, Seagrasses and Algae of the Philippines. Bookmark, 
Makati City, Philippines. 197 pp. 

SeagrassNet team has clearly shown the impacts of 
eutrophication at the site adjacent to a coastal town. 
Seagrass-Watch is now established in Puerto Galera. 
This community-based seagrass monitoring program 
is coordinating with SeagrassNet to provide a second 
data stream, generated by volunteer members. 


There are 11 species of seagrass in Viet Nam distributed 
along the coastline but mostly from the middle to the 
southern sections. Their status is unknown though in 
general the Viet Nam coastal zone has been heavily 
impacted by sedimentation and domestic and 
agricultural pollution. Viet Nam has at least 440 km? of 
seagrasses determined from remote sensing and 
ground-truth surveys. Viet Nam is at the overlap of 
temperate and tropical seagrass species with Zostera 
japonica growing intertidally in the north and mixing 
with Halophila ovalis, while in the south the species 
composition is similar to the Philippines and Malaysia. 


Miguel Fortes, Marine Science Institute CS, University of the Philippines, 
Diliman, Quezon City 1101, Philippines. Tel: + 63 (0}2 9205301. Fax: +63 
(0}2 9247678. E-mail: mdfortes138( 

Ed Green, UNEP World Conservation Monitoring Centre, 219 Huntingdon 
Road, Cambridge CB3 ODL, UK. 

Fred Short, University of New Hampshire, Jackson Estuarine Laboratory, 
85 Adams Point Road, Durham, NH 03824, USA. 

9 Merrill ED [1912]. A Flora of Manila. Philippine Islands Bureau of 
Science Publication Number 5. Bureau of Printing, Manila. 490 pp. 

10 Phillips RC, Mefiez EG [1988]. Seagrasses. Smithsonian 
Contributions to the Marine Sciences No. 34. 104 pp. 

11 Calumpong HP, Mefez EG, Phillips RC [1986]. Seagrasses in 
Batanes Province, northern Philippines. Silliman Journal 33(1-4): 

12 Dolar MLL [1991]. A survey on the fish and crustacean fauna of the 
seagrass beds in North Bais Bay, Negros Oriental, Philippines. In: 
Proceedings of the Regional Symposium on Living Resources in 
Coastal Areas. University of the Philippines Marine Science 
Institute, Quezon City. pp 367-377. 

13 Leptein MV [1992]. The gut passage rate and daily food 
consumption of the rabbitfish Siganus canaliculatus {Park}. In: 
Third ASEAN Science and Technology Week Conference 
Proceedings Vol. 6. National University of Singapore and National 
Science Technology Board, Singapore. pp. 327-336. 

14 Calumpong HP, Phillips RC, Menez EG, Estacion JS, de Leon ROD, 
Alava MNR [1993]. Performance of seagrass transplants in Negros 
Island, central Philippines and its implications in mitigating 
degraded shallow coastal areas. In: Proceedings of the 2nd RP- 
USA Phycology Symposium/Workshop. Philippine Council for 
Aquatic and Marine Research and Development, Los Banos, 
Laguna. pp 295-313. 

17 The seagrasses of 


ate (Zosteraceae] species and nine tropical 

species (Hydrocharitaceae and Cymodoceaceae}, 
occur on the coasts of Japan, about a quarter of the 
total number of seagrass species in the world [Table 
17.1). Species diversity is high not only for seagrasses 
but also for algal flora, with about 1500 species of 
algae occurring around Japan. Such a high species 
diversity in Japanese marine flora is probably related to 
complex hydrodynamic properties around the Japanese 
coasts that are affected by several major ocean 
currents such as the Oyashio cold current, and the 
Kuroshio and Tsushima warm currents. 

Among the 16 species of seagrasses in Japan, 
nine belong to the families Hydrocharitaceae and 
Cymodoceaceae and are tropical species commonly 
found in tropical and subtropical areas of the Indo-West 
Pacific region'”. In Japan, their distribution is restricted 
to the southwestern islands (Ryukyu and Amami 
Islands) except for Halophila ovalis. In contrast, 
distribution of all the species of Zosteraceae Is limited 
to the main island areas, except for Zostera japonica 
which also occurs in the Ryukyu Islands. Thus, the 
seagrass flora in Japan differ distinctly between the 
subtropical southwestern islands and the temperate 
coasts of the main islands. The southern limit of the 
temperate species of Zosteraceae is determined by the 
summer high seawater temperature of 28°C around 
Kyushu, while the distribution of tropical seagrass 
species is restricted by the winter seawater 
temperature of 15°C”. 

Along the temperate coasts of China, the Korean 
Peninsula and the islands of Japan, species diversity of 
Zosteraceae is high. In addition to Zostera marina, a 
cosmopolitan species widespread in the northern 
hemisphere in both the Pacific and Atlantic Oceans, six 
species of the family Zosteraceae are present that are 
considered to be endemic to the northwestern Pacific 
(Japanese, Korean, Chinese and southeast Russian 

S ixteen seagrass species, including seven temper- 


K. Aioi 
M. Nakaoka 

waters], namely Zostera asiatica, Zostera caespitosa, 
Zostera caulescens, Zostera japonica, Phyllospadix 
iwatensis and Phyllospadix japonicus®“’. The region can 
be regarded as a “hotspot” of seagrass floral diversity 
within the temperate waters of the northern 
hemisphere. Most of these species have limited 
distribution in some localities along the northern part 
of Japan (see below). The hemispheric distributions in 
the western Pacific may reflect the speciation process 
of Zosteraceae from its possible ancestral origins in 
equatorial regions". 

Despite the high species diversity of Japanese 
seagrasses, there are relatively few ecological studies 
of these species with the exception of Zostera marina. 
After pioneer studies by Tomitaro Makino and Shigeru 
Miki who described these species in the late 19th and 
early 20th centuries, few seagrass studies were 
conducted in Japan until the early 1970s. This is 
especially true for the endemic species of Zosteraceae 
for which information on distribution and ecology was 
not available until recently, partly due to their 
occurrence in deep water {see below). 

Eelgrass, Zostera marina, is a cosmopolitan 
species commonly found in temperate to subarctic 
coasts in the northern hemisphere". In Japan, Zostera 
marina occurs in numerous localities along the 
coastlines of the main islands, i.e. Honshu, Hokkaido, 
Kyushu and Shikoku“. The northernmost population of 
Zostera marina in Japan is found near Soya Cape, 
Hokkaido (45°30'N] and the southernmost population 
in Satsuma Peninsula, Kyushu [(31°10'N)'”. Most 
eelgrass populations in Japan are perennial and extend 
their distribution both by clonal propagation of 
rhizomes and by seed production, although an annual 
form of Zostera marina is found in some localities such 
as Hamana-ko, Okayama and Kagoshima®”. 

Zostera japonica is a small seagrass that 
generally inhabits intertidal and shallow subtidal 
bottoms along the coast of East Asia, from Viet Nam to 




Sakhalin and Kamchatka, Russia'’". In Japan, Zostera 
japonica is found in various localities, such as Notsuke 
Bay in the northeastern part of Hokkaido'", Toyama 
Bay in the Sea of Japan'’*“, Sagami Bay on the Pacific 
coast of central Honshu'’ and the Ryukyu Islands, in 
the southwestern part of Japan'*"*. 

Zostera asiatica was originally recorded by Miki 
from southern Sakhalin (Russia), the northeastern and 
southern parts of Hokkaido, in the central part of 
Honshu facing the Sea of Japan, and on the eastern 
coast of the Korean Peninsula”. In Japan, populations 
of Zostera asiatica are currently known only in 
Hamanaka and Akkeshi Bay, Hokkaido”, and in 
Funakoshi Bay, on the northeastern coast of Honshu”. 
Additionally, the stranded dead plants have been 
collected at several beaches in Hokkaido and one site in 
Toyama Bay". 

Zostera caulescens was known from limited 
localities along the central to northern coast of Honshu 
and the southern coast of the Korean Peninsula when 
Miki first described this species'’”". Some recent 
papers report the existence of populations in Mutsu 
Bay, northern Honshu", along the Sanriku coast, 
northeastern Honshu'***", in Tokyo Bay and Sagami 

Table 17.1 
Seagrasses recorded in Japan 

Species Distribution 

Enhalus acoroides 
Thalassia hemprichii 
Halophila decipiens 
Halophila ovalis 

Ryukyu Islands 
Ryukyu Islands 
Ryukyu Islands 
From Ryukyu Islands to 
central Honshu 

Cymodocea rotundata 
Cymodocea serrulata 
Halodule pinifolia 
Halodule uninervis 
Syringodium isoetifolium 

Ryukyu Islands 
Ryukyu Islands 
Ryukyu Islands 
Ryukyu Islands 
Ryukyu Islands 

Phyllospadix iwatensis 
Phyllospadix japonicus 
Zostera asiatica 
Zostera caespitosa 
Zostera caulescens 
Zostera japonica 

North Honshu and Hokkaido 
South Honshu 

Hokkaido and north Honshu 
Hokkaido and north Honshu 
Central and north Honshu 
From Ryukyu Islands to 

Zostera marina From Kyushu to Hokkaido 

(2, 15, 24-26) 

Bay, on the Pacific coast of central Honshu and 

in Toyama Bay, on the Sea of Japan'™”’. 

Zostera caespitosa was reported to occur in 
Hokkaido, in the northern half of Honshu and on the 
east of the Korean Peninsula’. Populations of this 
species were recently reported from Notoro Lake and 
Notsuke Bay in Hokkaido"®*”, Mutsu Bay, northern 
Honshu”, Yamada Bay and Otsuchi Bay, northeastern 
Honshu”, and Toyama Bay, in the Sea of Japan'™’. 

Two Phyllospadix species, Phyllospadix iwatensis 
and Phyllospadix japonicus, inhabit the intertidal and 
subtidal rocky bottoms of temperate regions of Japan. 
Distribution of Phyllospadix iwatensis ranges from 
Hokkaido to the northern part of Honshu. Phyllospadix 
japonicus occurs in the central part of the Pacific coast 
of Honshu and the western part of the Sea of Japan 
coast of Honshu’. 

Among the nine tropical seagrass species 
belonging to the families Hydrocharitaceae and 
Cymodoceaceae, Halophila ovalis has the widest 
distribution, occurring from the Yaeyama Islands to 
Chiba Prefecture [Odawa Bay) and to Toyama Bay, on 
the Sea of Japan'”. The distribution of the other eight 
species is restricted to the Amami and Ryukyu Islands 
(Table 17.1}. Detailed information on island-by-island 
distribution of each species has been given!” *:*). 

Geographical distribution of these species 
overlaps widely, with multispecific seagrass habitats 
commonly observed both in the temperate and tropical 
regions of Japan. In Hokkaido, three species coexist in 
a single bed in Notoro-ko (Zostera marina, Zostera 
japonica and Zostera caespitosa) and in Akkeshi Bay 
(Zostera marina, Zostera asiatica and Phyllospadix 
iwatensis}. In Honshu, four seagrass species co-occur 
in Odawa Bay (Zostera marina, Zostera japonica, 
Zostera caulescens and Halophila ovalis)'“’ and in 
Otsuchi Bay (Zostera marina, Zostera caespitosa, 
Zostera caulescens and Phyllospadix iwatensis), and 
three species co-occur in Funakoshi Bay (Zostera 
marina, Zostera asiatica and Zostera caulescens) and 
in lida Bay (Zostera marina, Zostera japonica and 
Zostera caespitosa). In the Ryukyu Islands, nine 
species were found in a single seagrass bed in Iriomote 
Island (Enhalus acoroides, Thalassia hemprichii, 
Halophila ovalis, Cymodocea rotundata, Cymodocea 
serrulata, Halodule pinifolia, Halodule uninervis, 
Syringodium isoetifolium and Zostera japonica)'”’; eight 
species were found in some beds at Ishigaki Island, 
Miyako Island and Okinawa Island"? ****, 


The depth range of seagrasses in Japan is reported for 
some multispecific seagrass beds where two or more 
species coexist in a single bed’. Generally, each 
species in the mixed beds shows a different depth 

distribution, forming some specific patterns of zonation 
along depth gradients. 

Among Zostera spp. in temperate multispecific 
seagrass meadows, Zostera japonica |s always found in 
the uppermost parts of the bed, as its main habitat is 
intertidal flats. Zostera marina occurs in the shallowest 
parts of subtidal beds, mostly between 1 and 5 m deep, 
but in some places down to 10 m. Zostera asiatica 
occurs between the intertidal zone and a depth of 5 m. 
Two other species generally occur in deeper habitats 
than Zostera marina: Zostera caespitosa, between 1 
and 20 m, and Zostera caulescens, between 3 and 17m. 
In most of the mixed seagrass beds, the plants’ depth 
ranges overlap to some degree with Zostera marina. 
Depth zonation in Zostera asiatica, Zostera caespitosa 
and Zostera caulescens cannot be described since 
these species do not generally co-occur. 

In multispecific seagrass beds in the Ryukyu 
Islands, Halodule pinifolia, Cymodocea rotundata and 
Thalassia hemprichii are dominant in the intertidal to 
upper subtidal zone, while Cymodocea serrulata and 
Enhalus acoroides are more abundant in the deeper 
subtidal zone'**". The observed depth distribution of 
these species generally agrees with those reported in 
other parts of the tropical Indo-West Pacific region”. 

Quantitative studies on biomass, shoot density, 
shoot size and productivity have been conducted in 
about 30 seagrass beds in Japan. Biomass, shoot 
density and shoot size of Zostera marina vary greatly 
among and within populations. Within populations, 
biomass, shoot density and shoot size have sometimes 
varied more than twofold, with greater biomass 
generally observed in shallower parts of seagrass 
beds’”“". Biomass as high as 500 g dry weight/m’ was 
recorded in some areas such as Notsuke Bay, Otsuchi 
Bay, Ushimado and Maizuru Bay, whereas maximum 
biomass was less than 200 g dry weight/m’ for 
populations in Odawa Bay, Yanai Bay and Toyama 
Bay’. Estimates for above-ground net production were 
available for several Zostera marina populations, and 
varied between less than 1 g to 13 g dry weight/m’/day 
at different sites, depths and seasons. Between-site 
variation in these parameters did not appear to be 
correlated with variations in latitude or geographical 

Quantitative information on abundance and 
productivity is very sparse for other species of Zostera, 
and for the tropical seagrass species, in Japan. 
Biomass of Zostera japonica varies greatly with season; 
a maximum biomass of 270 g dry weight/m? was 
recorded in July and a minimum of 30 g dry weight/m* 
from December to January at Mikawa Bay, the Pacific 
side of central Honshu". For Zostera caespitosa, 
maximum above-ground biomass of 60 g dry weight/m’ 
was recorded for the population in lida Bay, Noto 



Notsuke Bay 
Hokkaido “ee 

“Akkeshi Bay 
4— Mutsu Bay . 
~~ DPR E SEA OF JAPAN e Yamada Bay 
“KOREA * Tope Bay Funakoshi Bay 
he Tie Bae) Otsuchi Bay 
4 Ly; Maizuru Bay > Honshu 
SEA ~ 
5 oe dl Okavertecz 3 Odawa Buy 
> of \ Sagumi Bay 
Kyichut iliag Shikoku Iamana-ko 
Kagoshima > Seto Inland Sea 
EAST oh 
. Amami ls 
Ryukyu Is. 
Okinawa Island 0 200 400 600 Kilometers 
@ **Yaeyama Is 
Map 17.1 

Peninsula (the Sea of Japan coast)”. For Zostera 

asiatica at Akkeshi Bay, Hokkaido, biomass (427 g dry 
weight/m’] was twice that of Zostera marina, whereas 
the shoot density (134 shoots/m’) was about half of 
Zostera marina when comparing monospecific stands 
at the same depth, reflecting the larger shoot size of 
the former”. The above-ground net production of 
Zostera asiatica was estimated to be 3-5 g dry 

Information on the flowering and fruiting seasons 
of Zostera marina and other Zostera species is 
available from some localities in Japan’. In Zostera 
marina, seasons for flowering and fruiting vary by 2-4 
months across the region, with early flowering and 
fruiting observed at lower latitudes. Seed germination 
of Zostera marina was generally observed during the 
winter in southern populations and during spring in 
northern populations. For other Zostera species, 
flowering and fruiting seasons have been reported only 
from limited localities, and vary greatly among 

pS hes 

Photo: K. Aioi 




localities. For Zostera asiatica and Zostera caulescens, 
the flowering and fruiting seasons are generally the 
same as those of coexisting Zostera marina, whereas 
Zostera caespitosa flowers and fruits about one month 

earlier than sympatric Zostera marina™’. 


Although seagrasses have been very familiar to, and 
traditionally utilized by, Japanese people living in 
coastal areas, very little information is available about 

Table 17.2 
Traditional uses of seagrasses in Japan 

Traditional use Species Locality 
Rope for gill net Phyllospadix iwatensis Hokkaido 
Cushions for horse Zostera marina Sanriku 
saddles (Miyagi Pre.] 
Fishermen's skirts  Phyllospadix iwatensis Sanriku 

and Zostera marina _|wate Pre.) 
Cushions for train Zostera marina Tokyo Bay area 
Seto Inland Sea 
Miura Peninsula 
(Kanagawa Pre.) 

Tatami mats Zostera marina 
Agricultural compost Algae and 
Zostera marina 
Agricultural compost Algae and Zostera 
marina (Shizuoka Pre.) 
Agricultural compost Zostera marina Mikawa Bay 
Agricultural compost Zostera marina Seto Inland Sea 
(Okayama Pre.] 
(Shimane Pre.) 

Agricultural compost Zostera marina and 
freshwater plants 

Note: Pre. = Prefecture. 

Table 17.3 

Estimates of total areas of algal and seagrass beds in 
Japan in 1978 and 1991, and the percent area lost during 
the period 

Area of macrophyte Arealost % 
beds (km’] (km?) lost 
1978 1991 
Algal beds* 2748 2664 83 3.0 
Seagrass beds 515 495 21 4.0 
Total 3263 3159 104 3.2 

Note: * Algal beds consisted of Ulva, Enteromorpha, 
Sargassum, Laminaria, Eisenia and Gelidium.. 

Source: As reported by the Japanese Environment Agency in 1994. 

the historical distribution of seagrass beds. In Tokyo 
Bay, an old chart issued in 1908 shows the distribution 
of Zostera marina and Zostera japonica in the early 
20th century. Extensive seagrass meadows of 
approximately 3-5 km’ in area were located in shallow 
waters (<3 m] in some localities such as Yokohama, 
Tokyo, Funabashi and Chiba’. Unfortunately, all these 
seagrass beds were destroyed in land reclamation 
(filling and hardening of the shoreline] projects during 
industrialization in the mid-20th century. 

Traditional uses of seagrasses in Japan include 
direct use as fiber for rope or padding (e.g. cushions 
and tatami mats] or use as agricultural compost (Table 
17.2). Besides those listed, there may well be further 
traditional uses. For example, eelgrass was named 
moshiogusa in Japanese, which means salt grass, and 
might have been used to produce salt. 


The area of seagrass beds, especially those consisting 
of eelgrass Zostera marina, has declined since the 
1960s, mainly because of land reclamation. During 
these last decades, the Japanese economy has 
developed rapidly. The Environment Agency of Japan 
surveyed the status of algal and seagrass beds along 
most of the coastal areas of Japan in 1978 and again in 
1991, from which the loss during this period was 
estimated (Table 17.3]. The total area of algal and 
seagrass beds together was 3262 km’ in 1978 and 
3 159 km? in 1991. For seagrass beds, the total area 
declined from 515 km* to 495 km’ during the period, i.e. 
about 4 percent of Japan's total seagrass resource was 
lost in 13 years. In particular, more than 30 percent of 
Zostera marina beds disappeared in localities such as 
Ariake Bay, Kagoshima Bay and Hyuga-nada in Kyushu 
during this period”. In the Seto Inland Sea, more than 
70 percent of Zostera marina beds have been lost since 
1977, a loss which has seriously affected coastal 

For regionally endemic species of Zostera, the 
situation may be more serious than for Zostera marina, 
because populations are now known to exist in only a 
few localities around Japan. In fact, Zostera asiatica and 
Zostera caulescens are now ranked as VU [vulnerable 
stage] in the Red Data Book of threatened Japanese 
plant species. Among tropical seagrass species, 
Enhalus acoroides and Halophila decipiens are found 
only in limited localities in the Ryukyu Islands, and they 
are also listed as VU in the Red Data Book. 


As described above, seagrasses have been 
disappearing rapidly due to industrial development in 
the coastal regions of Japan. Major threats for further 

Case Study 17.1 

In Hokkaido, the northernmost island of Japan, 
some healthy Zostera marina beds remain. At 
Akkeshi [(42°50'N, 144°50'E), located in eastern 
Hokkaido, extensive seagrass meadows occur in 
Akkeshi-ko (a brackish lagoon) adjacent to Akkeshi 
Bay. In Akkeshi-ko, the dominant seagrass is 
Zostera marina with minor amounts of Zostera 
Japonica. A large-scale study was recently initiated 
here to examine the interactions between terrestrial 
and coastal ecosystems. It was found that 
considerable amounts of nutrients of terrestrial 
origin flow into this lagoon and these are important 
for the productivity of Zostera marina and associated 
communities. Studies on food web dynamics in the 
Zostera marina bed have revealed that the major 
consumer of Zostera marina was the whooper swan 
(Cygnus cygnus) which overwinters in the lagoon, 
and that mysids are the most dominant herbivores 
grazing on epiphytic algae on eelgrass”. Both the 
biomass and the diversity of mysids are high, and 
this supports high productivity of commercially 
important fish and shellfish species such as 
epifaunal shrimps and several species of fish®”. 

decline in present seagrass coverage include land 
reclamation, environmental deterioration such as 
reduced water quality, and rise in water temperature 
and water level due to global warming. 

The loss of seagrass vegetation over the last two 
decades along the Japanese coast is mostly attributed 
to land reclamation’. Many land reclamation projects 
are still ongoing or at the planning stage, and will 
probably further accelerate the loss of seagrass beds. 
For example, the coastline has been damaged by land 
reclamation and port construction in the Ryukyu 
Islands where large economic investments have been 
made toward rapid modernization. The natural 
ecosystems of coral reefs and lagoons were greatly 
impacted, especially along the coasts of Okinawa 
Island. Dugongs inhabit several seagrass beds in the 
northeastern coast of Okinawa Island, which is the 
northern limit of global distribution of this threatened 
marine mammal. Nevertheless, a large-scale land 
reclamation project is now planned in the center of the 
seagrass beds (Henoko coral lagoon) to build an 
offshore runway for the US air base. Such construction 
would almost certainly be fatal to the lagoon ecosystem 
and directly destroy seagrass habitats for dugongs. The 
Environment Agency of Japan decided to make a 
general survey of the northernmost dugongs and their 


Photo: C. Hily 

Zostera marina leaves coated with epiphytes 

habitats in February 2002. Scientists and non- 
governmental organizations in Japan must support and 
collaborate in these surveys to save the dugongs and 
conserve their habitats. 

Some seagrass beds have been declining rapidly 
even in areas where no major land reclamation has 
occurred, such as the Seto Inland Sea. In these areas, 
water pollution and disturbance of habitats by fish 
trawling are major causes of decline in seagrass beds. 

In the case of multispecific seagrass meadows, 
changes in environmental conditions due to human 
activities have effects not only on overall seagrass 
distribution and abundance but also on the species 
composition of the seagrass beds. In Odawa Bay near 
the Tokyo metropolitan area, for example, reduced light 
condition due to eutrophication over the past 20 years 
caused a decrease in areas of Zostera marina in 
shallow habitats, but possibly favored the deeper-living 
Zostera caulescens to expand its populations into 
shallower depths'. However, due to lack of species- 
by-species data in past literature, it is not possible to 
determine whether Zostera caulescens truly increased 
in recent years. Long-term field surveys of seagrass 
beds using a unified approach are necessary in order to 
monitor future changes in seagrasses in relation to 
changes in environmental conditions. 




Photo: K. Aioi 

Case Study 17.2 

Five temperate seagrass species, Zostera marina, 
Zostera caulescens, Zostera caespitosa, Zostera 
Japonica and Phyllospadix iwatensis, occur in the 
three bays along the Rias Coast facing the 
northeastern Pacific, namely Yamada Bay, 
Funakoshi Bay and Otsuchi Bay, in lwate Prefecture. 
The species composition of seagrasses varies 
among the bays. In Yamada Bay, Zostera caespitosa 
is the most abundant, with Zostera marina co- 
occurring. The dominant species in the seagrass 
bed in Funakoshi Bay is Zostera caulescens with 
small patches of Zostera marina and Zostera 
asjatica occurring at the shallower part of the bed. 
Zostera caulescens, Zostera marina and Zostera 
caespitosa are found to coexist in several seagrass 
beds in Otsuchi Bay. 

A large-scale census of these seagrass beds 
has been undertaken using an acoustic sounding 

The world’s longest seagrass, Zostera caulescens, at 10 m 
deep in Funakoshi Bay. 

technique to estimate overall distribution and 
abundance of seagrasses®. The survey in 
Funakoshi Bay has shown that the areal extent of the 
seagrass bed was approximately 0.5 km? with the 
depth distribution extending from 2 to 17 m. 
Variation in canopy height of Zostera caulescens by 
depth was also analyzed from the echo-trace of the 
sounder. The same technique has been utilized to 
estimate the abundance of Zostera caespitosa in 
Yamada Bay and to monitor long-term changes in 
patch dynamics of a seagrass bed at a river mouth 
on Otsuchi Bay. 

In the seagrass bed at Funakoshi Bay, Zostera 
caulescens develops a high canopy at the deeper 
parts of the bed (>10 m) by extending long flowering 
shoots. A maximum shoot height of 6.8 m was 
recorded in 1998, known as the world’s record 
longest among all seagrasses”. In July 2000, an 
even longer shoot (7.8 m] was found at the same 
site. Studies of the dynamics and production of the 
Zostera caulescens population revealed that most of 
the flowering shoots emerge in winter and grow 
rapidly, reaching an average height of 5 m in late 
summer, Annual above-ground net production per 
area was estimated to be 426 g dry weight/m’/year, 
similar to estimates for other Zostera species that 
live in intertidal and shallow subtidal beds {<1 m 
deep). Thus, the productivity of Zostera caulescens 
iS quite high despite its distribution in deep water [4- 
6 m) with poor light conditions. Comparative 
morphological and phenological studies of Zostera 
caulescens between Iwate and Sangami Bay {near 
Tokyo] showed that the large differences in shoot 
height and seasonal dynamics are probably related 
to differences in environmental factors such as 

In these seagrass beds, the abundance and 
dynamics of associated communities have been 
investigated for epiphytic algae, sessile 
epifauna'™, mobile epifauna®*****' and benthic 
infauna®”. The dynamics of these organisms are 
greatly influenced by spatial and temporal variations 
in seagrass abundance. Most interestingly, a species 
of tanaid crustacean (Zeuxo sp.) was found to feed 
on predispersal seeds of Zostera marina and 
Zostera caulescens™. The crustacean consumes up 
to 30 percent of the seeds, which may have a large 
negative impact on the seed abundance of the 

The global circulation of ocean currents is 

important not only for land vegetation but also for 
marine plants, as distributions of temperate and 
tropical seagrass species are restricted by seawater 
temperature in summer and winter, respectively, along 
the Japanese archipelago. Most physicists and meteor- 
ologists believe that the seas have warmed from 2°C to 
5°C over the past 50 years due to global warming. 
Global warming is predicted to affect the photosynthetic 
activities of marine plants in Japan. A further warming 
of 2 or 3°C in the seawater temperature may prove fatal 
to seagrass beds in shallower areas”. Shallow water 
vegetation such as seagrass and algae along the coasts 
of Japan is also at risk of accelerated loss due to water 
level rise caused by global warming. 





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18 The seagrasses of 

The Republic of Korea 


of the Eurasian continent, lies between 33°N and 

43°N. The total coastline of the peninsula, 
including the coastlines of the islands, reaches 
17000 km. About 3400 islands are distributed along the 
coasts of the Republic of Korea. Since each coast shows 
very distinct characteristics, seagrass habitat 
properties also vary. The west and the south coasts 
have highly complex and indented coastlines, while the 
east coast has a simple and linear one. Sand dunes are 
well developed, and several lagoons are formed on the 
east coast of the peninsula. Tidal flats are located at 
several places on the south coast. Tidal range is 1-4 m 
on the south coast and higher along the west part of the 
coastline. About 2000 islands are distributed in the 
western part of the south coast. Although the linear 
distance of the west coast is some 650 km, the actual 
length of the coastline is about 4700 km. Tidal range is 
extremely high on the west coast of the Korean 
peninsula; maximum tidal range is about 10 m on this 
coast. Very large tidal flats are formed because of the 
flat sea bottom and high tidal range. 

Eight temperate seagrass species, five Zostera, 
two Phyllospadix and Ruppia maritima, are distributed 
on the coasts of the Korean peninsula’. Although 
seagrasses are relatively abundant, few studies have 
reported on their physiology and ecology in this area 
and most of these reports were written in the Korean 
language. In this paper, we review the status, habitat 
characteristics and ecology of seagrasses on the coasts 
of the Republic of Korea. 

The Korean peninsula is enclosed by the Yellow 
Sea (to the west of Korea], the South Sea and the East 
Sea, which have considerably different characteristics 
(Table 18.1]. The coastline of the Yellow Sea [the west 
coast] shows a heavily indented coast with maximum 
tidal range of about 10 m. The hydrographic properties 
and circulation characteristics of the Yellow Sea are 
strongly influenced by climatic conditions. The South 

Ty: Korean peninsula, located at the eastern end 

K.-S. Lee 
S.Y. Lee 

Sea is connected to the East China Sea and the 
Tsushima current, a branch of Kuroshio, flows towards 
the East Sea through the South Sea. The coastline of 
the South Sea is also heavily indented. Tidal ranges on 
the south coast vary from about 1.0 m in the east part 
of the coast to about 4.0 m in the west part. The East 
Sea is deeper than the Yellow Sea or the South Sea, and 
the eastern coastline is very simple and linear. Tidal 
range Is usually less than 0.3 m. 


Eight temperate seagrass species are distributed on 
the coasts of the Korean peninsula. Zostera marina is 
the most abundant seagrass species, widely distributed 
throughout all coastal areas (Table 18.2) in relatively 
large meadows. Zostera asiatica is mostly distributed 
in the cold and temperate coasts of northeastern Asia. 
In the Republic of Korea Zostera asiatica occurs on the 
east coast; the distribution of this species on the west 
and the south coasts of the Korean peninsula is not 
clear. Zostera caespitosa, Zostera caulescens and 
Zostera japonica are found on all the Republic of 
Korea's coasts (Table 18.2). 

Two Phyllospadix species, Phyllospadix iwatensis 
and Phyllospadix japonicus, are found on Korean 
coasts”. Phyllospadix japonicus occurs on all coasts of 
the peninsula, while Phyllospadix iwatensis occurs on 
the east and west coasts. On the east coast, 
Phyllospadix iwatensis usually appears in the northern 
parts of the coast, while Phyllospadix japonicus is 
distributed in the southern parts. Distribution of Ruppia 
maritima in the Republic of Korea has been reported 
from limited areas on the west and south coasts"””. 


Seagrasses are distributed in numerous locations 
along the coast of the Korean peninsula with habitat 
types varying among the different coasts (Table 18.3). 
Seagrasses are widely distributed throughout the south 



Table 18.1 
Physical characteristics of seagrass beds on the west, south and east coasts of the Republic of Korea 

Characteristics West coast 
Wave energy Low 

Sediment Muddy sand